CN120676154A

CN120676154A - Image encoding/decoding method and device

Info

Publication number: CN120676154A
Application number: CN202511117943.7A
Authority: CN
Inventors: 姜晶媛; 李河贤; 林成昶; 李镇浩; 金晖容; 全炳宇; 朴智允
Original assignee: Sungkyunkwan University School Industry Cooperation; Electronics and Telecommunications Research Institute ETRI
Current assignee: Sungkyunkwan University School Industry Cooperation; Electronics and Telecommunications Research Institute ETRI
Priority date: 2019-06-25
Filing date: 2020-06-25
Publication date: 2025-09-19
Also published as: CN120676156A; WO2020262992A1; KR20210000689A; CN113906754A; CN120676155A; CN113906754B; US20220321915A1

Abstract

An image encoding/decoding method and apparatus are disclosed. The image decoding method includes obtaining sub-block-based transform (SBT) usage information, obtaining at least one of SBT division information, SBT division direction information, or SBT position information when the SBT usage information indicates that SBT is used, and performing SBT on a current block based on at least one of the SBT division information, the SBT division direction information, or the SBT position information. When the width of the current block and the height of the current block are smaller than the maximum transform size, SBT usage information may be obtained.

Description

Image encoding/decoding method and apparatus

The application is a divisional application of an application patent application with the application number of 202080040583.4 and the title of image coding/decoding method and device, which is 25 days of the application of 2020 and 06 months.

Technical Field

The present invention relates to an image encoding/decoding method and apparatus, and a recording medium for storing a bitstream. More particularly, the present invention relates to an image encoding/decoding method and apparatus using sub-block based transform (SBT).

Background

Recently, in various applications, demands for high resolution and high quality images such as High Definition (HD) or Ultra High Definition (UHD) images have increased. As the resolution and quality of images increase, the amount of data correspondingly increases. This is one of the reasons for the increase in transmission costs and storage costs when image data is transmitted through an existing transmission medium such as a wired or wireless broadband channel or when image data is stored. In order to solve these problems of high resolution and high quality image data, efficient image encoding/decoding techniques are required.

There are various video compression techniques such as an inter-prediction technique that predicts a value of a pixel within a current picture from a value of a pixel within a previous picture or a subsequent picture, an intra-prediction technique that predicts a value of a pixel within one region of a current picture from a value of a pixel within another region of a current picture, a transformation and quantization technique that compresses energy of a residual signal, and an entropy encoding technique that assigns shorter codes to frequently occurring pixel values and longer codes to less occurring pixel values.

There are various compression techniques that can be used to encode an image. Furthermore, depending on the nature of the image to be encoded, certain techniques may be more advantageous than others. Thus, the encoder may perform the most advantageous compression by adaptively determining whether a variety of compression techniques are used for the corresponding block. To select the most advantageous compression technique for the corresponding block from among the alternative techniques, the encoder may perform a Rate Distortion Optimization (RDO) process. Since it is not possible to know in advance which of the various encoding determinations can be selected to encode an image, an encoder applying the rate-distortion optimization technique may mainly use a method of performing encoding (or simplifying encoding) for each of all possible combinations of image encoding determinations, calculating its rate-distortion (RD) value, and setting an image encoding determination having the smallest of the calculated rate-distortion values as a final encoding determination for a corresponding block. After the encoder finally determines which technique to use or which technique to use, the encoder needs to signal to the decoder in order to perform the appropriate decoding. However, since separate information is transmitted (or signaled) for signaling, additional bits are used and thus compression performance may be reduced. Therefore, a technique capable of improving compression efficiency and providing an optimal image quality for a reconstructed image while minimizing the amount of bits for transmitting individual information is required.

In addition, inter prediction is known to be very effective for predictive coding of images. In general, since an object in each picture (or frame) image constituting a video sequence does not move very rapidly, there is a very high correlation between pictures unless a screen change occurs. To use this, when inter-frame differential encoding is used in the time axis direction using the motion prediction encoding technique, temporal redundancy can be removed, and thus very high encoding efficiency can be obtained. The encoding using the correlation between pictures arranged in the time axis direction is called inter prediction. Such an inter prediction method enables random access, and thus greatly contributes to an improvement in coding efficiency together with an intra prediction coding method capable of improving the fault tolerance of a coded bitstream.

The residual signal obtained by intra prediction or inter prediction is compressed by transformation and quantization, and then is compressed by entropy encoding using an arithmetic encoder such as CABAC. However, in the residual signal obtained after prediction, it may not be necessary to frequently transform all signals (e.g., pixels) of the corresponding block. However, if the conventional transform technique is used, the entire residual signal block obtained through prediction should be transformed, and thus, low compression efficiency may occur. This problem can be avoided by performing prediction on the further divided blocks. However, in this case, since the block is further subdivided, additional bits are required to signal the block division.

Disclosure of Invention

Technical problem

The invention aims to provide a sub-block-based transformation method and device.

The present invention is directed to a method and apparatus for compressing and constructing encoded information for sub-block based transforms into a compressed bitstream.

The present invention is directed to a method and apparatus for efficiently performing block transform in consideration of the shape and size of a block in sub-block-based transform coding.

The present invention is directed to a method and apparatus for efficiently performing a block transform in consideration of the shape and size of a block in decoding a sub-block-based transform.

Further, the present invention is directed to a recording medium for storing a bitstream generated by an image encoding/decoding method or apparatus.

Technical proposal

An image decoding method according to the present invention includes obtaining sub-block based transform (SBT) usage information, obtaining at least one of SBT division information, SBT division direction information, or SBT position information when the SBT usage information indicates that SBT is used, and performing SBT on a current block based on at least one of the SBT division information, the SBT division direction information, or the SBT position information. When the width of the current block and the height of the current block are smaller than the maximum transform size, SBT usage information is obtained.

In the image decoding method, the SBT division information may indicate a method of dividing a current block for the SBT, the SBT division direction information may indicate a division direction for the SBT, and the SBT position information may indicate which sub-block among sub-blocks divided from the current block is transformed based on the SBT division information and the SBT division direction information.

In the image decoding method, the step of obtaining the SBT use information may include deriving context model information of the SBT use information, and performing entropy decoding based on the context model information to obtain the SBT use information.

In the image decoding method, the deriving context model information of the SBT usage information may include deriving the context model information of the SBT usage information based on whether an area of the current block is greater than or equal to a predefined value.

In the image decoding method, the predefined value may be 256.

An image encoding method according to the present invention may include determining whether a sub-block based transform (SBT) is used for a current block, encoding SBT usage information based on the determination, and encoding at least one of SBT partition information, SBT partition direction information, or SBT position information when the SBT usage information indicates that SBT is used. When the width of the current block and the height of the current block are smaller than the maximum transform size, the SBT usage information is encoded.

In the image encoding method, the SBT division information may indicate a method of dividing a current block for the SBT, the SBT division direction information may indicate a division direction for the SBT, and the SBT position information may indicate which sub-block among sub-blocks divided from the current block is transformed based on the SBT division information and the SBT division direction information.

In the image encoding method, the step of encoding the SBT use information may include determining context model information of the SBT use information and performing entropy encoding based on the context model information to encode the SBT use information.

In the image encoding method, the determining of the context model information of the SBT use information may include determining the context model information of the SBT use information based on whether an area of the current block is greater than or equal to a predefined value.

In the image encoding method, the predefined value may be 256.

Further, the recording medium according to the present invention may store a bitstream generated by the image encoding method according to the present invention.

Advantageous effects

The present invention can improve coding efficiency and subjective image quality by providing an improved coding and decoding method and apparatus for image coding and decoding using sub-block based transforms.

Further, according to the present invention, it is possible to provide a recording medium for storing a bitstream generated by an image encoding/decoding method or apparatus.

Furthermore, according to the present invention, image encoding and decoding efficiency can be improved.

Drawings

Fig. 1 is a block diagram showing a configuration of an encoding apparatus according to an embodiment to which the present invention is applied.

Fig. 2 is a block diagram showing a configuration of a decoding apparatus to which the present invention is applied according to an embodiment.

Fig. 3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded.

Fig. 4 is a diagram illustrating intra prediction processing.

Fig. 5 is a diagram illustrating an embodiment of inter prediction processing.

Fig. 6 is a diagram showing a transformation and quantization process.

Fig. 7 is a diagram illustrating reference samples that can be used for intra prediction.

Fig. 8 is a view showing an example of division of CUs as encoding units.

Fig. 9 is a diagram illustrating eight SBT modes according to an embodiment of the present invention.

FIG. 10 is a diagram showing a method for signaling a cu_sbt_flag, a cu_sbt_quad_flag cu_sbt_horizontal flag and cu_sbt diagram of syntax of_pos_flag.

Fig. 11 is a diagram showing a method of implementing embodiment 1 of the present invention.

Fig. 12 is a diagram showing another method of implementing embodiment 1 of the present invention.

Fig. 13 is a diagram showing a method of implementing embodiment 2 of the present invention.

Fig. 14 is a diagram illustrating a 1/4-split SBT mode according to an embodiment of the present invention.

Fig. 15 is a diagram illustrating an embodiment of determining the context of the cu_sbt_quad_flag.

Fig. 16 is a diagram illustrating a sub-block division direction according to a shape of a CU according to an embodiment of the present invention.

Fig. 17 is a diagram showing the shape and sub-block division direction of a CU according to an embodiment of the present invention.

Fig. 18 is a diagram illustrating an embodiment of selectively signaling a cu_sbt_horizontal_flag.

Fig. 19 is a diagram illustrating a shape of a CU and an SBT mode according to an embodiment of the present invention.

Fig. 20 is a diagram illustrating an embodiment of determining a context of the cu_sbt_horizontal_flag (or sbtHorFlag).

Fig. 21 is a diagram illustrating an embodiment of a context determination method for entropy encoding (or decoding) of SBT information.

Fig. 22 to 25 are diagrams illustrating a context determination method of CABAC encoding/decoding according to various embodiments of the present invention.

Fig. 26 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

Fig. 27 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.

Detailed Description

Various modifications may be made to the present invention and various embodiments of the present invention exist, examples of which will now be provided and described in detail with reference to the accompanying drawings. However, the present invention is not limited thereto, and although the exemplary embodiments may be construed as including all modifications, equivalents, or alternatives falling within the technical spirit and scope of the present invention. In various aspects, like reference numerals refer to the same or similar functionality. In the drawings, the shape and size of elements may be exaggerated for clarity. In the following detailed description of the invention, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure. It is to be understood that the various embodiments of the disclosure, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, and characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the spirit and scope of the disclosure. Further, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled.

The terms "first," "second," and the like, as used in the specification, may be used to describe various components, but the components should not be construed as limited to these terms. These terms are only used to distinguish one component from another. For example, a "first" component may be named a "second" component, and a "second" component may also be similarly named a "first" component, without departing from the scope of the invention. The term "and/or" includes a combination of items or any of a plurality of items.

It will be understood that in the present specification, when an element is referred to simply as being "connected" or "coupled" to another element, it can be "directly connected" or "directly coupled" to the other element or be connected or coupled to the other element with other elements interposed therebetween. In contrast, it will be understood that when an element is referred to as being "directly coupled" or "directly connected" to another element, there are no intervening elements present.

Further, constituent parts shown in the embodiments of the present invention are independently shown to represent feature functions different from each other. Therefore, this does not mean that each constituent part is constituted by a separate constituent unit of hardware or software. In other words, for convenience, each constituent part includes each of the enumerated constituent parts. Thus, at least two constituent parts of each constituent part may be combined to form one constituent part, or one constituent part may be divided into a plurality of constituent parts to perform each function. Embodiments in which each constituent part is combined and embodiments in which one constituent part is divided are also included in the scope of the present invention without departing from the spirit of the present invention.

The terminology used in the description presented herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Unless the context clearly differs, a statement that is used in the singular includes a plural form of statement. In this specification, it will be understood that terms such as "comprises," "comprising," "includes," "including," and the like are intended to indicate the presence of features, numbers, steps, actions, elements, components, or combinations thereof disclosed in the specification, but are not intended to exclude the possibility that one or more other features, numbers, steps, actions, elements, components, or combinations thereof may be present or added. In other words, when a particular element is referred to as being "included," it is not intended to exclude elements other than the corresponding element, but additional elements may be included in the embodiments of the invention or the scope of the invention.

Furthermore, some components may not be indispensable components for performing the basic functions of the present invention, but only selective components that enhance the performance thereof. The present invention may be realized by including only an essential component for realizing the essence of the present invention and not including a component for improving performance. Structures that include only the essential components and not only the optional components for performance enhancement are also included within the scope of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Well-known functions or constructions are not described in detail in describing exemplary embodiments of the invention since they would unnecessarily obscure the invention. The same constituent elements in the drawings are denoted by the same reference numerals, and repetitive description of the same elements will be omitted.

Hereinafter, an image may refer to a picture constituting a video, or may refer to a video itself. For example, "encoding or decoding an image or both encoding and decoding" may refer to "encoding or decoding a moving picture or both encoding and decoding" and may refer to "encoding or decoding one of the images of a moving picture or both encoding and decoding".

Hereinafter, the terms "moving picture" and "video" may be used as the same meaning and may be replaced with each other.

Hereinafter, the target image may be an encoding target image as an encoding target and/or a decoding target image as a decoding target. Further, the target image may be an input image input to the encoding apparatus, and an input image input to the decoding apparatus. Here, the target image may have the same meaning as the current image.

Hereinafter, the terms "image", "picture", "frame" and "screen" may be used as the same meaning and may be replaced with each other.

Hereinafter, the target block may be an encoding target block as an encoding target and/or a decoding target block as a decoding target. Further, the target block may be a current block that is a target of current encoding and/or decoding. For example, the terms "target block" and "current block" may be used as the same meaning and may be replaced with each other.

Hereinafter, the terms "block" and "unit" may be used as the same meaning and may be replaced with each other. Or a "block" may represent a particular unit.

Hereinafter, the terms "region" and "fragment" may be replaced with each other.

Hereinafter, the specific signal may be a signal representing a specific block. For example, the original signal may be a signal representing a target block. The prediction signal may be a signal representing a prediction block. The residual signal may be a signal representing a residual block.

In an embodiment, each of the specific information, data, flags, indexes, elements, attributes, etc. may have a value. The value of the information, data, flags, indexes, elements, and attributes equal to "0" may represent a logical false or a first predefined value. In other words, the value "0", false, logical false, and the first predefined value may be replaced with each other. The value of the information, data, flags, indexes, elements, and attributes equal to "1" may represent a logical true or a second predefined value. In other words, the values "1", true, logical true, and second predefined values may be substituted for each other.

When the variable i or j is used to represent a column, row, or index, the value of i may be an integer equal to or greater than 0, or an integer equal to or greater than 1. That is, columns, rows, indexes, etc. may start counting from 0, or may start counting from 1.

Description of the terms

Encoder-means the device performing the encoding. That is, the encoding device is represented.

Decoder-representing the device performing the decoding. That is, the decoding apparatus is represented.

The block is an array of M x N samples. Here, M and N may represent positive integers, and a block may represent a sample array in a two-dimensional form. A block may refer to a unit. The current block may represent an encoding target block that becomes a target at the time of encoding or a decoding target block that becomes a target at the time of decoding. Further, the current block may be at least one of a coded block, a predicted block, a residual block, and a transformed block.

The samples are the basic units constituting the block. Depending on the bit depth (B _d), the samples can be represented as values from 0 to 2 ^Bd -1. In the present invention, a sample may be used as a meaning of a pixel. That is, the sample, pel, and pixel may have the same meaning as each other.

Unit may refer to an encoding and decoding unit. When encoding and decoding an image, a unit may be a region generated by partitioning a single image. Further, when a single image is partitioned into sub-divided units during encoding or decoding, the units may represent the sub-divided units. That is, the image may be partitioned into a plurality of units. When encoding and decoding an image, predetermined processing for each unit may be performed. A single cell may be partitioned into sub-cells having a size smaller than the size of the cell. According to functions, a unit may represent a block, a macroblock, a coding tree unit, a coding tree block, a coding unit, a coding block, a prediction unit, a prediction block, a residual unit, a residual block, a transform unit, a transform block, and the like. Further, to distinguish a unit from a block, the unit may include a luma component block, a chroma component block associated with the luma component block, and a syntax element for each color component block. The cells may have various sizes and shapes, in particular, the shape of the cells may be a two-dimensional geometry, such as square, rectangular, trapezoidal, triangular, pentagonal, etc. Further, the unit information may include at least one of a unit type indicating an encoding unit, a prediction unit, a transformation unit, and the like, a unit size, a unit depth, an order of encoding and decoding of the unit, and the like.

The coding tree unit is configured with a single coding tree block of the luminance component Y and two coding tree blocks associated with the chrominance components Cb and Cr. Furthermore, the coding tree unit may represent a syntax element including a block and each block. Each of the encoding tree units may be partitioned by using at least one of a quadtree partitioning method, a binary tree partitioning method, and a trigeminal tree partitioning method to configure a lower level unit such as an encoding unit, a prediction unit, a transform unit, or the like. The coding tree unit may be used as a term for specifying a block of samples that becomes a processing unit when an image that is an input image is encoded/decoded. Here, the quadtree may represent a quad tree.

When the size of the encoded block is within a predetermined range, division using only quadtree partitions is possible. Here, the predetermined range may be defined as at least one of a maximum size and a minimum size of the encoded block that can be divided using only the quadtree partition. Information indicating the maximum/minimum size of the encoded blocks allowing the quadtree partitioning may be signaled through a bitstream, and may be signaled in at least one unit of a sequence, a picture parameter, a parallel block group, or a slice (slice). Alternatively, the maximum/minimum size of the encoded block may be a predetermined fixed size in the encoder/decoder. For example, when the size of the encoded block corresponds to 256×256 to 64×64, division using only quadtree partitions is possible. Alternatively, when the size of the encoded block is larger than the size of the maximum conversion block, it is possible to divide using only quadtree partitions. Here, the block to be divided may be at least one of an encoding block and a transform block. In this case, the information indicating the division of the encoded block (e.g., split_flag) may be a flag indicating whether to perform quadtree partitioning. When the size of the encoded block falls within a predetermined range, division using only binary tree or trigeminal tree partitions is possible. In this case, the above description of the quadtree partition may be applied to the binary tree partition or the trigeminal tree partition in the same manner.

Coding tree block-may be used as a term for specifying any one of a Y coding tree block, a Cb coding tree block, and a Cr coding tree block.

Neighboring blocks-may represent blocks adjacent to the current block. The blocks adjacent to the current block may represent blocks that are in contact with the boundary of the current block or blocks that are located within a predetermined distance from the current block. The neighboring block may represent a block adjacent to the vertex of the current block. Here, a block adjacent to a vertex of the current block may represent a block vertically adjacent to an adjacent block horizontally adjacent to the current block, or a block horizontally adjacent to an adjacent block vertically adjacent to the current block.

The neighboring block may be reconstructed-may represent a neighboring block that is adjacent to the current block and has been spatially/temporally encoded or decoded. Here, the reconstruction neighboring block may represent a reconstruction neighboring unit. The reconstructed spatial neighboring block may be a block that is within the current picture and has been reconstructed by encoding or decoding or both. The reconstruction-time neighboring block is a block at a position within the reference picture corresponding to the current block of the current picture or a neighboring block of the block.

The cell depth is a measure of the extent to which a cell is partitioned. In a tree structure, the highest node (root node) may correspond to the first unit that is not partitioned. Further, the highest node may have a minimum depth value. In this case, the depth of the highest node may be level 0. A node of depth level 1 may represent a unit generated by partitioning a first unit once. A node of depth level 2 may represent a unit generated by partitioning the first unit twice. A node of depth level n may represent a unit generated by partitioning the first unit n times. The leaf node may be the lowest node and is a node that cannot be partitioned further. The depth of the leaf node may be the maximum level. For example, the predefined value of the maximum level may be 3. The depth of the root node may be lowest and the depth of the leaf node may be deepest. Furthermore, when a cell is represented as a tree structure, the level at which the cell exists may represent the cell depth.

Bit stream-a bit stream comprising encoded image information may be represented.

The parameter set corresponds to header information among the configurations within the bitstream. At least one of a video parameter set, a sequence parameter set, a picture parameter set, and an adaptive parameter set may be included in the parameter set. Further, the parameter set may include a slice header, a parallel block (tile) group header, and parallel block header information. The term "parallel block group" denotes a group of parallel blocks and has the same meaning as a stripe.

The adaptive parameter set may represent a parameter set that may be shared by being referenced in different pictures, sprites, slices, parallel blocks, or partitions (blocks). Furthermore, the information in the adaptive parameter set may be used by referring to different adaptive parameter sets for sub-pictures, slices, parallel block groups, parallel blocks or partitions within a picture.

Further, with respect to the adaptive parameter sets, the different adaptive parameter sets may be referenced by using identifiers for the different adaptive parameter sets of the sub-picture, slice, parallel block group, parallel block, or partition within the picture.

Further, regarding the adaptive parameter sets, the different adaptive parameter sets may be referred to by using identifiers for the different adaptive parameter sets of the slice, parallel block group, parallel block, or partition within the sprite.

Furthermore, with respect to the adaptive parameter sets, the different adaptive parameter sets may be referenced by using identifiers of the different adaptive parameter sets for parallel blocks or partitions within the stripe.

Further, with respect to the adaptive parameter sets, the different adaptive parameter sets may be referenced by using identifiers of the different adaptive parameter sets for the partitions within the parallel blocks.

Information about the adaptive parameter set identifier may be included in a header or a parameter set of the sprite, and the adaptive parameter set corresponding to the adaptive parameter set identifier may be used for the sprite.

Information about the adaptive parameter set identifier may be included in a header or a parameter set of the parallel block, and the adaptive parameter set corresponding to the adaptive parameter set identifier may be used for the parallel block.

Information about the adaptive parameter set identifier may be included in the header of the block, and the adaptive parameter set corresponding to the adaptive parameter set identifier may be used for the block.

A picture may be partitioned into one or more parallel block rows and one or more parallel block columns.

A sprite may be partitioned into one or more parallel rows of blocks and one or more parallel columns of blocks within the picture. A sprite may be an area within a picture that has a rectangular/square form and may include one or more CTUs. Further, at least one or more parallel blocks/partitions/stripes may be included within one sprite.

The parallel block may be an area within a picture having a rectangular/square form and may include one or more CTUs. Further, the parallel blocks may be partitioned into one or more partitions.

A chunk may represent one or more CTU rows within a parallel chunk. The parallel blocks may be partitioned into one or more partitions, and each partition may have at least one or more CTU rows. Parallel blocks that are not partitioned into two or more may represent partitions.

The stripe may include one or more parallel blocks within a picture and may include one or more partitions within the parallel blocks.

Parsing may represent determining a value of a syntax element by performing entropy decoding, or may represent entropy decoding itself.

The symbol may represent at least one of a syntax element, an encoding parameter, and a transform coefficient value of an encoding/decoding target unit. Further, the symbol may represent an entropy encoding target or an entropy decoding result.

The prediction mode may be information indicating a mode encoded/decoded using intra prediction or a mode encoded/decoded using inter prediction.

The prediction unit may represent a basic unit when prediction such as inter prediction, intra prediction, inter compensation, intra compensation, and motion compensation is performed. A single prediction unit may be partitioned into a plurality of partitions having smaller sizes, or may be partitioned into a plurality of lower prediction units. The plurality of partitions may be basic units in performing prediction or compensation. The partition generated by dividing the prediction unit may also be the prediction unit.

Prediction unit partition-may represent a shape obtained by partitioning a prediction unit.

A reference picture list may refer to a list including one or more reference pictures for inter prediction or motion compensation. There are several types of available reference picture lists, including LC (list combination), L0 (list 0), L1 (list 1), L2 (list 2), L3 (list 3).

The inter prediction indicator may refer to a direction of inter prediction (unidirectional prediction, bidirectional prediction, etc.) of the current block. Alternatively, the inter prediction indicator may refer to the number of reference pictures used to generate a prediction block of the current block. Alternatively, the inter prediction indicator may refer to the number of prediction blocks used when performing inter prediction or motion compensation on the current block.

The prediction list utilization flag indicates whether to generate a prediction block using at least one reference picture in a particular reference picture list. The inter prediction indicator may be derived using the prediction list utilization flag, and conversely, the prediction list utilization flag may be derived using the inter prediction indicator. For example, when the prediction list utilization flag has a first value of zero (0), it indicates that reference pictures in the reference picture list are not used to generate the prediction block. On the other hand, when the prediction list utilization flag has a second value of one (1), it indicates that the reference picture list is used to generate the prediction block.

The reference picture index may refer to an index indicating a particular reference picture in a reference picture list.

The reference picture may represent a reference picture that is referenced by a particular block for the purpose of inter prediction or motion compensation of the particular block. Alternatively, the reference picture may be a picture including a reference block referenced by the current block for inter prediction or motion compensation. Hereinafter, the terms "reference picture" and "reference image" have the same meaning and are interchangeable.

The motion vector may be a two-dimensional vector for inter prediction or motion compensation. The motion vector may represent an offset between the encoding/decoding target block and the reference block. For example, (mvX, mvY) may represent a motion vector. Here, mvX may represent a horizontal component, and mvY may represent a vertical component.

The search range may be a two-dimensional region that is searched to retrieve a motion vector during inter prediction. For example, the size of the search range may be mxn. Here, M and N are integers.

The motion vector candidates may refer to prediction candidate blocks or motion vectors of the prediction candidate blocks when predicting the motion vectors. Further, the motion vector candidates may be included in a motion vector candidate list.

The motion vector candidate list may represent a list of one or more motion vector candidates.

The motion vector candidate index may represent an indicator indicating a motion vector candidate in the motion vector candidate list. Alternatively, it may be an index of the motion vector predictor.

The motion information may represent information including at least one of items including a motion vector, a reference picture index, an inter prediction indicator, a prediction list utilization flag, reference picture list information, a reference picture, a motion vector candidate index, a merge candidate, and a merge index.

The merge candidate list may represent a list composed of one or more merge candidates.

The merge candidates may represent spatial merge candidates, temporal merge candidates, combined bi-predictive merge candidates, or zero merge candidates. The merge candidates may include motion information such as an inter prediction indicator, a reference picture index of each list, a motion vector, a prediction list utilization flag, and an inter prediction indicator.

The merge index may represent an indicator indicating a merge candidate in the merge candidate list. Alternatively, the merge index may indicate a block in a reconstructed block spatially/temporally adjacent to the current block from which the merge candidate has been derived. Alternatively, the merge index may indicate at least one piece of motion information of the merge candidate.

A transform unit may represent a basic unit when encoding/decoding (such as transform, inverse transform, quantization, inverse quantization, transform coefficient encoding/decoding) is performed on the residual signal. A single transform unit may be partitioned into a plurality of lower transform units having smaller sizes. Here, the transformation/inverse transformation may include at least one of a first transformation/first inverse transformation and a second transformation/second inverse transformation.

Scaling may represent the process of multiplying the quantized level by a factor. Transform coefficients may be generated by scaling the quantized levels. Scaling may also be referred to as dequantization.

Quantization parameter-may represent a value used when a transform coefficient is used during quantization to generate a level of quantization. The quantization parameter may also represent a value used when generating transform coefficients by scaling the quantized level during dequantization. The quantization parameter may be a value mapped on the quantization step size.

Delta quantization parameter-the difference between the predicted quantization parameter and the quantization parameter of the encoding/decoding target unit can be represented.

Scanning may represent a method of ordering coefficients within a cell, block or matrix. For example, changing the two-dimensional matrix of coefficients to a one-dimensional matrix may be referred to as scanning, and changing the one-dimensional matrix of coefficients to a two-dimensional matrix may be referred to as scanning or inverse scanning.

Transform coefficients may represent coefficient values generated after a transform is performed in an encoder. The transform coefficient may represent a coefficient value generated after at least one of entropy decoding and inverse quantization is performed in the decoder. The quantized level obtained by quantizing the transform coefficient or the residual signal or the quantized transform coefficient level may also fall within the meaning of the transform coefficient.

The level of quantization may represent a value generated by quantizing a transform coefficient or a residual signal in an encoder. Alternatively, the level of quantization may represent a value that is an inverse quantization target subject to inverse quantization in the decoder. Similarly, quantized transform coefficient levels, which are the result of the transform and quantization, may also fall within the meaning of quantized levels.

Non-zero transform coefficients-may represent transform coefficients having values other than zero, or transform coefficient levels or quantized levels having values other than zero.

Quantization matrix-a matrix that may represent a matrix used in quantization processing or inverse quantization processing performed to improve subjective image quality or objective image quality. The quantization matrix may also be referred to as a scaling list.

Quantization matrix coefficients-each element within the quantization matrix may be represented. The quantized matrix coefficients may also be referred to as matrix coefficients.

The default matrix may represent a predetermined quantization matrix predefined in the encoder or decoder.

A non-default matrix may represent a quantization matrix that is not predefined in the encoder or decoder but signaled by the user.

Statistics the statistics for at least one of the variables, coding parameters, constant values, etc. having a computable specific value may be one or more of average, sum, weighted average, weighted sum, minimum, maximum, most frequently occurring value, median, interpolation for the specific value.

The encoding apparatus 100 may be an encoder, a video encoding apparatus, or an image encoding apparatus. The video may include at least one image. The encoding apparatus 100 may sequentially encode at least one image.

Referring to fig. 1, the encoding apparatus 100 may include a motion prediction unit 111, a motion compensation unit 112, an intra prediction unit 120, a switcher 115, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, an inverse quantization unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a reference picture buffer 190.

The encoding apparatus 100 may perform encoding of an input image by using an intra mode or an inter mode or both the intra mode and the inter mode. Further, the encoding apparatus 100 may generate a bitstream including encoded information by encoding an input image and output the generated bitstream. The generated bit stream may be stored in a computer readable recording medium or may be streamed over a wired/wireless transmission medium. When the intra mode is used as the prediction mode, the switcher 115 can switch to intra. Alternatively, when the inter mode is used as the prediction mode, the switcher 115 may switch to the inter mode. Here, the intra mode may represent an intra prediction mode, and the inter mode may represent an inter prediction mode. The encoding apparatus 100 may generate a prediction block for an input block of an input image. In addition, the encoding apparatus 100 may encode the residual block using the residuals of the input block and the prediction block after generating the prediction block. The input image may be referred to as a current image as a current encoding target. The input block may be referred to as a current block as a current encoding target or as an encoding target block.

When the prediction mode is an intra mode, the intra prediction unit 120 may use a sample of a block that has been encoded/decoded and is adjacent to the current block as a reference sample. The intra prediction unit 120 may generate prediction samples of the input block by performing spatial prediction on the current block using the reference samples, or by performing spatial prediction. Here, intra prediction may represent prediction inside a frame.

When the prediction mode is an inter mode, the motion prediction unit 111 may retrieve a region that best matches the input block from the reference image when performing motion prediction, and derive a motion vector by using the retrieved region. In this case, a search area may be used as the area. The reference picture may be stored in a reference picture buffer 190. Here, when encoding/decoding of the reference picture is performed, the reference picture may be stored in the reference picture buffer 190.

The motion compensation unit 112 may generate a prediction block by performing motion compensation on the current block using the motion vector. Here, the inter prediction may represent prediction or motion compensation between frames.

When the value of the motion vector is not an integer, the motion prediction unit 111 and the motion compensation unit 112 may generate a prediction block by applying an interpolation filter to a partial region of the reference picture. In order to perform inter-picture prediction or motion compensation on a coding unit, it may be determined which mode among a skip mode, a merge mode, an Advanced Motion Vector Prediction (AMVP) mode, and a current picture reference mode is used for motion prediction and motion compensation of a prediction unit included in a corresponding coding unit. Inter-picture prediction or motion compensation may then be performed differently according to the determined mode.

The subtractor 125 may generate a residual block by using a difference of the input block and the prediction block. The residual block may be referred to as a residual signal. The residual signal may represent a difference between the original signal and the predicted signal. Further, the residual signal may be a signal generated by transforming or quantizing or transforming and quantizing a difference between the original signal and the predicted signal. The residual block may be a residual signal of a block unit.

The transform unit 130 may generate transform coefficients by performing a transform on the residual block, and output the generated transform coefficients. Here, the transform coefficient may be a coefficient value generated by performing a transform on the residual block. When the transform skip mode is applied, the transform unit 130 may skip the transform of the residual block.

The level of quantization may be generated by applying quantization to transform coefficients or to the residual signal. Hereinafter, the level of quantization may also be referred to as a transform coefficient in an embodiment.

The quantization unit 140 may generate a quantized level by quantizing the transform coefficient or the residual signal according to the parameter, and output the generated quantized level. Here, the quantization unit 140 may quantize the transform coefficient by using a quantization matrix.

The entropy encoding unit 150 may generate a bitstream by performing entropy encoding on the values calculated by the quantization unit 140 or on the encoding parameter values calculated when encoding is performed according to a probability distribution, and output the generated bitstream. The entropy encoding unit 150 may perform entropy encoding on sample information of an image and information for decoding the image. For example, the information for decoding the image may include a syntax element.

When entropy encoding is applied, the symbols are represented such that a smaller number of bits are allocated to symbols having a high generation possibility and a larger number of bits are allocated to symbols having a low generation possibility, and thus, the size of a bit stream for symbols to be encoded can be reduced. The entropy encoding unit 150 may use an encoding method for entropy encoding such as exponential Golomb, context Adaptive Variable Length Coding (CAVLC), context Adaptive Binary Arithmetic Coding (CABAC), and the like. For example, the entropy encoding unit 150 may perform entropy encoding by using a variable length coding/coding (VLC) table. Further, the entropy encoding unit 150 may derive a binarization method of the target symbol and a probability model of the target symbol/binary bit, and perform arithmetic encoding by using the derived binarization method, probability model, and context model.

In order to encode the transform coefficient level (quantized level), the entropy encoding unit 150 may change coefficients in the form of a two-dimensional block into a one-dimensional vector form by using a transform coefficient scanning method.

The encoding parameters may include information (flags, indexes, etc.) such as syntax elements encoded in the encoder and signaled to the decoder, as well as information derived when encoding or decoding is performed. The encoding parameters may represent information required in encoding or decoding an image. For example, at least one value or combination of the following may be included in the encoding parameters, unit/block size, unit/block depth, unit/block partition information, unit/block shape, unit/block partition structure, whether to perform quad-tree type partitioning, whether to perform binary tree type partitioning, binary tree type partitioning direction (horizontal direction or vertical direction), binary tree type partitioning form (symmetric partitioning or asymmetric partitioning), whether the current encoding unit is partitioned by the trigeminal tree partitioning, trigeminal tree partitioning direction (horizontal direction or vertical direction), trigeminal tree partitioning type (symmetric type or asymmetric type), whether the current encoding unit is partitioned by the multi-type tree partitioning, and the like, the direction of the multi-type tree partition (horizontal direction or vertical direction), the type of the multi-type tree partition (symmetric type or asymmetric type), the tree (binary tree or trigeminal tree) structure of the multi-type tree partition, the prediction mode (intra-prediction or inter-prediction), the luminance intra-prediction mode/direction, the chrominance intra-prediction mode/direction, intra-frame partition information, inter-frame partition information, coding block partition flags, prediction block partition flags, transform block partition flags, reference sample point filtering methods, reference sample point filter taps, reference sample point filter coefficients, prediction block filtering methods, prediction block filter taps, prediction block filter coefficients, prediction block boundary filtering methods, Prediction block boundary filter tap, prediction block boundary filter coefficient, intra prediction mode, inter prediction mode, motion information, motion vector difference, reference picture index, inter prediction angle, inter prediction indicator, prediction list utilization flag, reference picture list, reference picture, motion vector predictor index, motion vector predictor candidate, motion vector candidate list, whether merge mode is used, merge index, merge candidate list, whether skip mode is used, interpolation filter type, interpolation filter tap, interpolation filter coefficient, motion vector size, accuracy of motion vector representation, and method of motion vector, The type of transform, the size of the transform, the information whether the primary (first) transform is used, the information whether the secondary transform is used, the primary transform index, the secondary transform index, the information whether a residual signal is present, the coding block pattern, the Coding Block Flag (CBF), the quantization parameters, the quantization parameter residuals, the quantization matrix, whether an intra loop filter is applied, the intra loop filter coefficients, the intra loop filter taps, the intra loop filter shape/form, whether a deblocking filter is applied, the deblocking filter coefficients, the deblocking filter taps, the deblocking filter strength, the deblocking filter shape/form, whether an adaptive sample offset is applied, the quantization parameter residuals, the quantization matrix, the intra loop filter is applied, the deblocking filter coefficients, the deblocking filter taps, the deblocking filter strength, the deblocking filter shape/form, the adaptive sample offset is applied, the quantization parameter residuals, the quantization matrix is applied, the quantization matrix is transformed, and the quantization matrix is transformed, An adaptive sample offset value, an adaptive sample offset class, an adaptive sample offset type, whether an adaptive in-loop filter is applied, an adaptive in-loop filter coefficient, an adaptive in-loop filter tap, an adaptive in-loop filter shape/form, a binarization/anti-binarization method, a context model determination method, a context model update method, whether a normal mode is performed, whether a bypass mode is performed, a context binary bit, a bypass binary bit, a significant coefficient flag, a last significant coefficient flag, an encoded flag for a unit of a coefficient group, a position of a last significant coefficient, a flag as to whether a value of a coefficient is greater than 1, a flag as to whether a value of a coefficient is greater than 2, A flag as to whether the value of the coefficient is greater than 3, information about the remaining coefficient value, sign information, reconstructed luminance sample point, reconstructed chroma sample point, residual luminance sample point, residual chroma sample point, luminance transform coefficient, chroma transform coefficient, quantized luminance level, quantized chroma level, transform coefficient level scanning method, size of motion vector search area on the decoder side, shape of motion vector search area on the decoder side, number of motion vector searches on the decoder side, information about CTU size, information about minimum block size, information about maximum block depth, information about minimum block depth, Image display/output order, slice identification information, slice type, slice partition information, parallel block identification information, parallel block type, parallel block partition information, parallel block group identification information, parallel block group type, parallel block group partition information, picture type, bit depth of input samples, bit depth of reconstructed samples, bit depth of residual samples, bit depth of transform coefficients, bit depth of quantized level, and information on luminance signals or information on chrominance signals.

Here, signaling a flag or index may mean that the corresponding flag or index is entropy encoded and included in the bitstream by the encoder, and may mean that the corresponding flag or index is entropy decoded from the bitstream by the decoder.

When the encoding apparatus 100 performs encoding through inter prediction, the encoded current image may be used as a reference image for another image that is subsequently processed. Accordingly, the encoding apparatus 100 may reconstruct or decode the encoded current image, or store the reconstructed or decoded image as a reference image in the reference picture buffer 190.

The quantized level may be inverse quantized in the inverse quantization unit 160 or may be inverse transformed in the inverse transformation unit 170. The inverse quantized or inverse transformed coefficients, or both, may be added to the prediction block by adder 175. The reconstructed block may be generated by adding the inverse quantized or inverse transformed coefficients or the inverse quantized and inverse transformed coefficients to the prediction block. Here, the inverse quantized or inverse transformed coefficient or the inverse quantized and inverse transformed coefficient may represent a coefficient on which at least one of the inverse quantization and inverse transformation is performed, and may represent a reconstructed residual block.

The reconstructed block may pass through a filter unit 180. The filter unit 180 may apply at least one of a deblocking filter, a Sample Adaptive Offset (SAO), and an adaptive in-loop filter (ALF) to a reconstructed sample, a reconstructed block, or a reconstructed image. The filter unit 180 may be referred to as an in-loop filter.

The deblocking filter may remove block distortion generated in boundaries between blocks. To determine whether to apply the deblocking filter, whether to apply the deblocking filter to the current block may be determined based on samples included in several rows or columns included in the block. When a deblocking filter is applied to a block, filters different from each other may be applied according to a required deblocking filter strength.

To compensate for coding errors, the appropriate offset value may be added to the sample value by using the sample adaptive offset. The sample adaptive offset may correct an offset of the deblocked image from the original image in units of samples. A method of applying the offset in consideration of edge information about each sample may be used, or a method of partitioning the sample of the image into a predetermined number of areas, determining an area to which the offset is applied, and applying the offset to the determined area may be used.

The adaptive in-loop filter may perform filtering based on a comparison of the filtered reconstructed image and the original image. The samples included in the image may be partitioned into predetermined groups, filters to be applied to each group may be determined, and differential filtering may be performed on each group. The information whether to apply the ALF may be signaled through a Coding Unit (CU), and the form and coefficients of the ALF to be applied to each block may vary.

The reconstructed block or the reconstructed image that has passed through the filter unit 180 may be stored in a reference picture buffer 190. The reconstructed block processed by the filter unit 180 may be part of a reference image. That is, the reference image is a reconstructed image composed of the reconstructed blocks processed by the filter unit 180. The stored reference pictures may be used later in inter prediction or motion compensation.

Fig. 2 is a block diagram showing the configuration of a decoding apparatus according to an embodiment and to which the present invention is applied.

The decoding apparatus 200 may be a decoder, a video decoding apparatus, or an image decoding apparatus.

Referring to fig. 2, the decoding apparatus 200 may include an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra prediction unit 240, a motion compensation unit 250, an adder 255, a filter unit 260, and a reference picture buffer 270.

The decoding apparatus 200 may receive the bit stream output from the encoding apparatus 100. The decoding apparatus 200 may receive a bitstream stored in a computer-readable recording medium, or may receive a bitstream streamed over a wired/wireless transmission medium. The decoding apparatus 200 may decode the bitstream by using an intra mode or an inter mode. Further, the decoding apparatus 200 may generate a reconstructed image or a decoded image generated by decoding and output the reconstructed image or the decoded image.

The switcher may be switched into the intra frame when the prediction mode used at the time of decoding is the intra frame mode. Alternatively, the switcher may be switched to the inter mode when the prediction mode used at the time of decoding is the inter mode.

The decoding apparatus 200 may obtain a reconstructed residual block by decoding an input bitstream and generate a prediction block. When the reconstructed residual block and the prediction block are obtained, the decoding apparatus 200 may generate a reconstructed block that is a decoding target by adding the reconstructed residual block and the prediction block. The decoding target block may be referred to as a current block.

The entropy decoding unit 210 may generate symbols by entropy decoding the bitstream according to the probability distribution. The generated symbols may include quantized, hierarchical forms of symbols. Here, the entropy decoding method may be an inverse process of the above-described entropy encoding method.

In order to decode the transform coefficient level (quantized level), the entropy decoding unit 210 may change the coefficient in the form of a one-way vector into a two-dimensional block form by using a transform coefficient scanning method.

The quantized levels may be dequantized in the dequantization unit 220, or the quantized levels may be inverse-transformed in the inverse transformation unit 230. The level of quantization may be the result of performing inverse quantization or inverse transformation or both, and may be generated as a reconstructed residual block. Here, the inverse quantization unit 220 may apply a quantization matrix to the quantized level.

When the intra mode is used, the intra prediction unit 240 may generate a prediction block by performing spatial prediction on the current block, wherein the spatial prediction uses sample values of blocks that are adjacent to the decoding target block and have been decoded.

When the inter mode is used, the motion compensation unit 250 may generate a prediction block by performing motion compensation on the current block, wherein the motion compensation uses a motion vector and a reference image stored in the reference picture buffer 270.

The adder 255 may generate a reconstructed block by adding the reconstructed residual block and the prediction block. The filter unit 260 may apply at least one of a deblocking filter, a sample adaptive offset, and an adaptive in-loop filter to the reconstructed block or the reconstructed image. The filter unit 260 may output the reconstructed image. The reconstructed block or reconstructed image may be stored in a reference picture buffer 270 and used when performing inter prediction. The reconstructed block processed by the filter unit 260 may be part of a reference image. That is, the reference image is a reconstructed image composed of the reconstructed blocks processed by the filter unit 260. The stored reference pictures may be used later in inter prediction or motion compensation.

Fig. 3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded. Fig. 3 schematically shows an example of partitioning a single unit into a plurality of subordinate units.

In order to partition an image efficiently, an encoding unit (CU) may be used when encoding and decoding. The encoding unit may be used as a basic unit when encoding/decoding an image. Further, the encoding unit may be used as a unit for distinguishing an intra prediction mode from an inter prediction mode in encoding/decoding an image. The coding unit may be a basic unit for prediction, transformation, quantization, inverse transformation, inverse quantization, or encoding/decoding processing of transform coefficients.

Referring to fig. 3, an image 300 is sequentially partitioned according to a maximum coding unit (LCU), and LCU units are determined as a partition structure. Here, LCU may be used in the same meaning as a Coding Tree Unit (CTU). A unit partition may represent a partition of a block associated with the unit. In the block partition information, information of a unit depth may be included. The depth information may represent the number or degree of times a unit is partitioned or both the number and degree of times a unit is partitioned. A single unit may be partitioned into a plurality of subordinate units hierarchically associated with depth information based on a tree structure. In other words, a unit and a lower level unit generated by partitioning the unit may correspond to a node and a child node of the node, respectively. Each of the partitioned subordinate units may have depth information. The depth information may be information representing the size of the CU, and may be stored in each CU. The cell depth represents the number and/or extent associated with partitioning a cell. Accordingly, the partition information of the lower unit may include information about the size of the lower unit.

The partition structure may represent a distribution of Coding Units (CUs) within LCU 310. Such a distribution may be determined according to whether a single CU is partitioned into multiple (positive integers equal to or greater than 2 including 2, 4, 8, 16, etc.) CUs. The horizontal and vertical sizes of the CUs generated by the partitioning may be half the horizontal and vertical sizes of the CUs before the partitioning, respectively, or may have sizes smaller than the horizontal and vertical sizes before the partitioning, respectively, according to the number of times of the partitioning. A CU may be recursively partitioned into multiple CUs. By recursive partitioning, at least one of the height and width of a CU after partitioning may be reduced compared to at least one of the height and width of a CU before partitioning. Partitioning of the CU may be performed recursively until a predefined depth or a predefined size. For example, the depth of the LCU may be 0 and the depth of the Smallest Coding Unit (SCU) may be a predefined maximum depth. Here, as described above, the LCU may be a coding unit having a maximum coding unit size, and the SCU may be a coding unit having a minimum coding unit size. The partitioning starts with LCU 310, and CU depth increases by 1 when the horizontal or vertical size or both the horizontal and vertical sizes of the CU are reduced by the partitioning. For example, for each depth, the size of an undivided CU may be 2n×2n. In addition, in the case of partitioned CUs, a CU having a size of 2n×2n may be partitioned into four CUs having a size of n×n. The size of n can be halved as depth increases by 1.

Further, information indicating whether or not a CU is partitioned may be used by using partition information of the CU. The partition information may be 1-bit information. All CUs except SCU may include partition information. For example, a CU may not be partitioned when the value of partition information is a first value, and a CU may be partitioned when the value of partition information is a second value.

Referring to fig. 3, an LCU having a depth of 0 may be a 64×64 block. 0 may be the minimum depth. The SCU with depth 3 may be an 8 x 8 block. 3 may be the maximum depth. A CU of a 32×32 block and a 16×16 block may be represented as depth 1 and depth 2, respectively.

For example, when a single coding unit is partitioned into four coding units, the horizontal and vertical sizes of the partitioned four coding units may be half the sizes of the horizontal and vertical sizes of the CU before being partitioned. In one embodiment, when a coding unit of size 32×32 is partitioned into four coding units, each of the partitioned four coding units may have a size of 16×16. When a single coding unit is partitioned into four coding units, it may be referred to as the coding units being partitioned into quadtree forms.

For example, when one coding unit is partitioned into two sub-coding units, the horizontal size or vertical size (width or height) of each of the two sub-coding units may be half of the horizontal size or vertical size of the original coding unit. For example, when a coding unit having a size of 32×32 is vertically partitioned into two sub-coding units, each of the two sub-coding units may have a size of 16×32. For example, when a coding unit having a size of 8×32 is horizontally partitioned into two sub-coding units, each of the two sub-coding units may have a size of 8×16. When a coding unit is partitioned into two sub-coding units, the coding units may be said to be partitioned or partitioned according to a binary tree partition structure.

For example, when one coding unit is partitioned into three sub-coding units, the horizontal or vertical sizes of the coding units may be partitioned in a ratio of 1:2:1, thereby generating three sub-coding units having a ratio of 1:2:1 in horizontal or vertical sizes. For example, when a coding unit having a size of 16×32 is horizontally partitioned into three sub-coding units, the three sub-coding units may have sizes of 16×8, 16×16, and 16×8, respectively, in order from the uppermost sub-coding unit to the lowermost sub-coding unit. For example, when a coding unit having a size of 32×32 is vertically divided into three sub-coding units, the three sub-coding units may have sizes of 8×32, 16×32, and 8×32, respectively, in order from the left side sub-coding unit to the right side sub-coding unit. When a coding unit is partitioned into three sub-coding units, the coding unit may be said to be partitioned by three or according to a trigeminal tree partition structure.

In fig. 3, a Coding Tree Unit (CTU) 320 is an example of a CTU in which a quadtree partition structure, a binary tree partition structure, and a trigeminal tree partition structure are all applied.

As described above, in order to partition the CTU, at least one of a quadtree partition structure, a binary tree partition structure, and a trigeminal tree partition structure may be applied. The various tree partition structures may be sequentially applied to the CTUs according to a predetermined priority order. For example, the quadtree partition structure may be preferentially applied to CTUs. Coding units that can no longer be partitioned using the quadtree partitioning structure may correspond to leaf nodes of the quadtree. The coding units corresponding to leaf nodes of the quadtree may be used as root nodes of the binary and/or trigeminal tree partition structures. That is, the coding units corresponding to leaf nodes of the quadtree may or may not be further partitioned in a binary tree partition structure or a trigeminal tree partition structure. Accordingly, by preventing the coding units obtained from the binary tree partition or the trigeminal tree partition of the coding units corresponding to the leaf nodes of the quadtree from undergoing further quadtree partition, the block partition operation and/or the operation of signaling partition information can be efficiently performed.

The fact that the coding units corresponding to the nodes of the quadtree are partitioned may be signaled using the quadtrees information. The quadtreeding information having a first value (e.g., "1") may indicate that the current coding unit is partitioned according to a quadtree partition structure. The quadtreeding information having a second value (e.g., "0") may indicate that the current coding unit is not partitioned according to the quadtree partition structure. The quarter-zone information may be a flag having a predetermined length (e.g., one bit).

There may be no priority between the binary tree partition and the trigeminal tree partition. That is, the coding units corresponding to the leaf nodes of the quadtree may further undergo any of the binary tree partitions and the trigeminal tree partitions. Furthermore, the coding units generated by binary tree partitioning or trigeminal tree partitioning may undergo further binary tree partitioning or further trigeminal tree partitioning, or may not be further partitioned.

The tree structure where no priority exists between the binary tree partition and the trigeminal tree partition is called a multi-type tree structure. The coding units corresponding to leaf nodes of the quadtree may be used as root nodes of the multi-type tree. At least one of the multi-type tree partition indication information, the partition direction information, and the partition tree information may be used to signal whether to partition the coding units corresponding to the nodes of the multi-type tree. In order to partition the coding units corresponding to the nodes of the multi-type tree, multi-type tree partition indication information, partition direction information, and partition tree information may be sequentially signaled.

The multi-type tree partition indication information having a first value (e.g., "1") may indicate that the current coding unit will experience multi-type tree partitions. The multi-type tree partition indication information having a second value (e.g., "0") may indicate that the current coding unit will not experience multi-type tree partitions.

When the coding units corresponding to the nodes of the multi-type tree are further partitioned in the multi-type tree partition structure, the coding units may include partition direction information. The partition direction information may indicate in which direction the current coding unit is to be partitioned for the multi-type tree partition. Partition direction information having a first value (e.g., "1") may indicate that the current coding unit is to be vertically partitioned. Partition direction information having a second value (e.g., "0") may indicate that the current coding unit is to be horizontally partitioned.

When the coding units corresponding to the nodes of the multi-type tree are further partitioned in accordance with the multi-type tree partition structure, the current coding unit may include partition tree information. The partition tree information may indicate a tree partition structure to be used to partition nodes of the multi-type tree. Partition tree information having a first value (e.g., "1") may indicate that the current coding unit is to be partitioned according to a binary tree partition structure. Partition tree information having a second value (e.g., "0") may indicate that the current coding unit is to be partitioned according to a trigeminal tree partition structure.

The partition indication information, partition tree information, and partition direction information may each be a flag having a predetermined length (e.g., one bit).

At least any one of the quadtree partition indication information, the multi-type tree partition indication information, the partition direction information, and the partition tree information may be entropy encoded/entropy decoded. To entropy encode/entropy decode those types of information, information about neighboring coding units that are adjacent to the current coding unit may be used. For example, the partition type (partitioned or not partitioned, partition tree, and/or partition direction) of the left neighboring coding unit and/or the upper neighboring coding unit of the current coding unit is highly likely to be similar to the partition type of the current coding unit. Accordingly, context information for entropy encoding/entropy decoding information about a current coding unit may be derived from information about neighboring coding units. The information on the neighboring coding units may include at least any one of quarter partition information, multi-type tree partition indication information, partition direction information, and partition tree information.

As another example, in the binary tree partition and the trigeminal tree partition, the binary tree partition may be preferentially executed. That is, the current coding unit may first go through the binary tree partition, and then the coding unit corresponding to the leaf node of the binary tree may be set as the root node for the trigeminal tree partition. In this case, neither the quadtree partition nor the binary tree partition may be performed for the coding units corresponding to the nodes of the trigeminal tree.

Coding units that cannot be partitioned in a quadtree partition structure, a binary tree partition structure, and/or a trigeminal tree partition structure become basic units for coding, prediction, and/or transformation. That is, the coding unit cannot be further partitioned for prediction and/or transformation. Thus, partition structure information and partition information for partitioning the coding unit into prediction units and/or transform units may not be present in the bitstream.

However, when the size of the coding unit (i.e., the basic unit for partitioning) is greater than the size of the maximum transform block, the coding unit may be partitioned recursively until the size of the coding unit is reduced to be equal to or less than the size of the maximum transform block. For example, when the size of the coding unit is 64×64 and when the size of the largest transform block is 32×32, the coding unit may be partitioned into four 32×32 blocks for the transform. For example, when the size of the coding unit is 32×64 and the size of the largest transform block is 32×32, the coding unit may be partitioned into two 32×32 blocks for the transform. In this case, the partition for transformation of the encoding unit is not separately signaled, and the partition for transformation of the encoding unit may be determined through comparison between the horizontal size or vertical size of the encoding unit and the horizontal size or vertical size of the maximum transformation block. For example, when the horizontal size (width) of the coding unit is greater than the horizontal size (width) of the maximum transform block, the coding unit may be vertically halved. For example, when the vertical size (height) of the coding unit is greater than the vertical size (height) of the maximum transform block, the coding unit may be horizontally halved.

Information of the maximum and/or minimum size of the coding unit and information of the maximum and/or minimum size of the transform block may be signaled or determined at an upper level of the coding unit. The upper level may be, for example, a sequence level, a picture level, a slice level, a parallel block group level, a parallel block level, etc. For example, the minimum size of the coding unit may be determined to be 4×4. For example, the maximum size of the transform block may be determined to be 64×64. For example, the minimum size of the transform block may be determined to be 4×4.

Information of the minimum size of the coding unit (minimum size of the quadtree) corresponding to the leaf node of the quadtree and/or information of the maximum depth from the root node of the multi-type tree to the leaf node (maximum tree depth of the multi-type tree) may be signaled or determined at an upper level of the coding unit. For example, the upper level may be a sequence level, a picture level, a slice level, a parallel block group level, a parallel block level, and the like. Information of the minimum size of the quadtree and/or information of the maximum depth of the multi-type tree may be signaled or determined for each of the intra-picture and inter-picture slices.

The difference information between the size of the CTU and the maximum size of the transform block may be signaled or determined at an upper level of the encoding unit. For example, the upper level may be a sequence level, a picture level, a slice level, a parallel block group level, a parallel block level, and the like. Information of a maximum size of the coding unit corresponding to each node of the binary tree (hereinafter, referred to as a maximum size of the binary tree) may be determined based on the size of the coding tree unit and the difference information. The maximum size of the coding units corresponding to the respective nodes of the trigeminal tree (hereinafter, referred to as the maximum size of the trigeminal tree) may vary according to the type of the stripe. For example, for intra-picture slices, the maximum size of the trigeminal tree may be 32×32. For example, for inter-picture slices, the maximum size of the trigeminal tree may be 128×128. For example, the minimum size of the coding unit corresponding to each node of the binary tree (hereinafter, referred to as the minimum size of the binary tree) and/or the minimum size of the coding unit corresponding to each node of the trigeminal tree (hereinafter, referred to as the minimum size of the trigeminal tree) may be set as the minimum size of the coding block.

As another example, the maximum size of the binary tree and/or the maximum size of the trigeminal tree may be signaled or determined at the stripe level. Alternatively, the minimum size of the binary tree and/or the minimum size of the trigeminal tree may be signaled or determined at the stripe level.

The four-partition information, the multi-type tree partition indication information, the partition tree information, and/or the partition direction information may or may not be included in the bitstream according to the above-described various block sizes and depth information.

For example, when the size of the coding unit is not greater than the minimum size of the quadtree, the coding unit does not include the quadbregion information. The quarter information may be inferred as a second value.

For example, when the size (horizontal and vertical) of the coding unit corresponding to the node of the multi-type tree is greater than the maximum size (horizontal and vertical) of the binary tree and/or the maximum size (horizontal and vertical) of the trigeminal tree, the coding unit may not be partitioned or trisected. Thus, the multi-type tree partition indication information may not be signaled, but may be inferred to be a second value.

Alternatively, when the size (horizontal size and vertical size) of the coding unit corresponding to the node of the multi-type tree is the same as the maximum size (horizontal size and vertical size) of the binary tree and/or twice as large as the maximum size (horizontal size and vertical size) of the trigeminal tree, the coding unit may not be further bi-partitioned or tri-partitioned. Thus, the multi-type tree partition indication information may not be signaled, but may be inferred to be a second value. This is because when the coding units are partitioned in a binary tree partition structure and/or a trigeminal tree partition structure, coding units smaller than the minimum size of the binary tree and/or the minimum size of the trigeminal tree are generated.

Alternatively, binary tree partitioning or trigeminal tree partitioning may be limited based on the size of the virtual pipeline data unit (hereinafter, pipeline buffer size). For example, when an encoding unit is divided into sub-encoding units that do not fit in the pipeline buffer size by a binary tree partition or a trigeminal tree partition, the corresponding binary tree partition or trigeminal tree partition may be restricted. The pipeline buffer size may be the size of the largest transform block (e.g., 64 x 64). For example, when the pipeline buffer size is 64×64, the following division may be limited.

N x M (N and/or M is 128) trigeminal tree partitioning for coding units

128 X N (N < =64) binary tree partitioning for the horizontal direction of the coding units

N×128 (N < =64) binary tree partitioning for the vertical direction of the coding units

Alternatively, when the depth of the coding unit corresponding to a node of the multi-type tree is equal to the maximum depth of the multi-type tree, the coding unit may not be further di-partitioned and/or tri-partitioned. Thus, the multi-type tree partition indication information may not be signaled, but may be inferred to be a second value.

Alternatively, the multi-type tree partition indication information may be signaled only when at least one of the vertical direction binary tree partition, the horizontal direction binary tree partition, the vertical direction trigeminal tree partition, and the horizontal direction trigeminal tree partition is possible for the coding unit corresponding to the node of the multi-type tree. Otherwise, the coding unit may not be partitioned and/or tri-partitioned. Thus, the multi-type tree partition indication information may not be signaled, but may be inferred to be a second value.

Alternatively, partition direction information may be signaled only when both vertical and horizontal binary tree partitions or both vertical and horizontal trigeminal tree partitions are possible for coding units corresponding to nodes of the multi-type tree. Otherwise, the partition direction information may not be signaled, but may be inferred as a value indicating a possible partition direction.

Alternatively, partition tree information may be signaled only when both vertical and vertical or horizontal binary and horizontal trigeminal tree partitions are possible for the coding tree corresponding to the nodes of the multi-type tree. Otherwise, the partition tree information may not be signaled, but may be inferred as values indicating possible partition tree structures.

Fig. 4 is a diagram illustrating intra prediction processing.

The arrow from the center to the outside in fig. 4 may represent the prediction direction of the intra prediction mode.

Intra-coding and/or decoding may be performed by using reference samples of neighboring blocks of the current block. The neighboring block may be a reconstructed neighboring block. For example, intra-coding and/or decoding may be performed by using values or coding parameters of reference samples included in reconstructed neighboring blocks.

The prediction block may represent a block generated by performing intra prediction. The prediction block may correspond to at least one of a CU, PU, and TU. The unit of the prediction block may have a size of one of the CU, PU, and TU. The prediction block may be a square block having a size of 2×2, 4×4, 16×16, 32×32, 64×64, or the like, or may be a rectangular block having a size of 2×8, 4×8, 2×16, 4×16, 8×16, or the like.

Intra prediction may be performed according to an intra prediction mode for the current block. The number of intra prediction modes that the current block may have may be a fixed value, and may be a value differently determined according to the attribute of the prediction block. For example, the attributes of the prediction block may include the size of the prediction block, the shape of the prediction block, and the like.

The number of intra prediction modes may be fixed to N regardless of the block size. Or the number of intra prediction modes may be 3, 5, 9, 17, 34, 35, 36, 65, 67, or the like. Alternatively, the number of intra prediction modes may vary according to a block size or a color component type or both the block size and the color component type. For example, the number of intra prediction modes may vary depending on whether the color component is a luminance signal or a chrominance signal. For example, as the block size becomes larger, the number of intra prediction modes may increase. Alternatively, the number of intra prediction modes of the luminance component block may be greater than the number of intra prediction modes of the chrominance component block.

The intra prediction mode may be a non-angular mode or an angular mode. The non-angular mode may be a DC mode or a planar mode, and the angular mode may be a prediction mode having a specific direction or angle. The intra prediction mode may be represented by at least one of a mode number, a mode value, a mode number, a mode angle, and a mode direction. The number of intra prediction modes may be M greater than 1, including non-angular modes and angular modes. For intra prediction of the current block, a step of determining whether a sample included in the reconstructed neighboring block can be used as a reference sample of the current block may be performed. When there is a sample that cannot be used as a reference sample of the current block, a value obtained by copying or performing interpolation or both of copying and interpolation on at least one sample value included in the samples in the reconstructed neighboring block may be used to replace an unavailable sample value of the sample, and thus the replaced sample value is used as a reference sample of the current block.

As shown in fig. 7, at least one of the reference sample line 0 to the reference sample line 3 may be used for intra prediction of the current block. In fig. 7, instead of retrieving from reconstructed neighboring blocks, the samples of segment a and segment F may be filled with the closest samples of segment B and segment E, respectively. Index information indicating a reference sample line to be used for intra prediction of the current block may be signaled. For example, in fig. 7, reference sample line indicators 0, 1, and 2 may be signaled as index information indicating reference sample line 0, reference sample line 1, and reference sample line 2. When the upper boundary of the current block is the boundary of the CTU, only the reference sample line 0 may be available. Therefore, in this case, the index information may not be signaled. When a reference sample line other than the reference sample line 0 is used, filtering for a prediction block, which will be described later, may not be performed.

When intra prediction is performed, a filter may be applied to at least one of the reference sample and the prediction sample based on at least one of the intra prediction mode and the current block size.

In the case of the planar mode, when generating a prediction block of a current block, a sample value of the prediction target sample point may be generated by using a weighted sum of an upper reference sample point and a left reference sample point of the current block and an upper right reference sample point and a lower left reference sample point of the current block according to a position of the prediction target sample point within the prediction block. Further, in case of the DC mode, when generating the prediction block of the current block, an average value of the upper reference sample and the left reference sample of the current block may be used. Further, in case of the angle mode, the prediction block may be generated by using an upper reference sample, a left reference sample, an upper right reference sample, and/or a lower left reference sample of the current block. To generate the predicted sample values, interpolation of real units may be performed.

In the case of intra prediction between color components, a prediction block of a current block of a second color component may be generated based on a corresponding reconstructed block of a first color component. For example, the first color component may be a luminance component and the second color component may be a chrominance component. For intra prediction between color components, parameters of a linear model between a first color component and a second color component may be derived based on a template. The template may comprise top and/or left neighboring samples of the current block and top and/or left neighboring samples of the reconstructed block of the first color component corresponding thereto. For example, parameters of the linear model may be derived using the sample values of the first color component having the largest value and the sample values of the second color component corresponding thereto in the samples in the template, and the sample values of the first color component having the smallest value and the sample values of the second color component corresponding thereto in the samples in the template. When deriving parameters of the linear model, a corresponding reconstructed block may be applied to the linear model to generate a prediction block for the current block. Depending on the video format, sub-sampling may be performed on neighboring samples of the reconstructed block of the first color component and the corresponding reconstructed block. For example, when one sample of the second color component corresponds to four samples of the first color component, the four samples of the first color component may be sub-sampled to calculate one corresponding sample. In this case, parameter derivation of the linear model and intra prediction between color components may be performed based on the corresponding sub-sampled samples. Whether to perform intra prediction between color components and/or the range of templates may be signaled as an intra prediction mode.

The current block may be partitioned into two sub-blocks or four sub-blocks in a horizontal direction or a vertical direction. The partitioned sub-blocks may be reconstructed sequentially. That is, intra prediction may be performed on sub-blocks to generate sub-prediction blocks. Further, inverse quantization and/or inverse transform may be performed on the sub-blocks to generate sub-residual blocks. The reconstructed sub-block may be generated by adding the sub-prediction block to the sub-residual block. The reconstructed sub-block may be used as a reference point for intra prediction of a subsequent sub-block. The sub-block may be a block including a predetermined number (e.g., 16) or more samples. Thus, for example, when the current block is an 8×4 block or a 4×8 block, the current block may be partitioned into two sub-blocks. Further, when the current block is a 4×4 block, the current block may not be partitioned into sub-blocks. When the current block has other sizes, the current block may be partitioned into four sub-blocks. Information about whether intra prediction is performed based on the sub-block and/or partition direction (horizontal or vertical) may be signaled. The sub-block-based intra prediction may be limited to be performed only when the reference sample line 0 is used. When sub-block-based intra prediction is performed, filtering for a prediction block, which will be described later, may not be performed.

The final prediction block may be generated by performing filtering on the prediction block that is intra-predicted. The filtering may be performed by applying a predetermined weight to the filtering target sample point, the left reference sample point, the upper reference sample point, and/or the upper left reference sample point. The weights and/or reference samples (range, position, etc.) for filtering may be determined based on at least one of the block size, intra prediction mode, and the position of the filtering target samples in the prediction block. The filtering may be performed only in the case of a predetermined intra prediction mode (e.g., DC, planar, vertical, horizontal, diagonal, and/or adjacent diagonal modes). The adjacent diagonal pattern may be a pattern in which k is added to or subtracted from the diagonal pattern. For example, k may be a positive integer of 8 or less.

The intra prediction mode of the current block may be entropy encoded/entropy decoded by predicting the intra prediction mode of a block existing adjacent to the current block. When the intra prediction mode of the current block and the neighboring block are identical, information of the current block identical to the intra prediction mode of the neighboring block may be signaled by using predetermined flag information. In addition, indicator information of the same intra prediction mode as the intra prediction mode of the current block among the intra prediction modes of the plurality of neighboring blocks may be signaled. When the intra prediction modes of the current block and the neighboring block are different, the intra prediction mode information of the current block may be entropy encoded/entropy decoded by performing entropy encoding/entropy decoding based on the intra prediction modes of the neighboring block.

Fig. 5 is a diagram illustrating an embodiment of inter prediction processing.

In fig. 5, a rectangle may represent a screen. In fig. 5, an arrow indicates a prediction direction. Depending on the coding type of a picture, the picture can be classified into an intra picture (I picture), a predicted picture (P picture), and a bi-predicted picture (B picture).

I-pictures can be encoded by intra prediction without inter-picture prediction. P pictures may be encoded through inter-picture prediction by using reference pictures existing in one direction (i.e., forward or backward) with respect to the current block. B pictures can be encoded through inter-picture prediction by using reference pictures existing in both directions (i.e., forward and backward) with respect to the current block. When inter-picture prediction is used, an encoder may perform inter-picture prediction or motion compensation, and a decoder may perform corresponding motion compensation.

Hereinafter, an embodiment of inter-picture prediction will be described in detail.

Inter-picture prediction or motion compensation may be performed using reference pictures and motion information.

The motion information of the current block may be derived during inter prediction by each of the encoding apparatus 100 and the decoding apparatus 200. The motion information of the current block may be derived by using motion information of a reconstructed neighboring block, motion information of a co-located block (also referred to as col block or co-located block), and/or motion information of a block adjacent to the co-located block. The co-located block may represent a block within a previously reconstructed co-located picture (also referred to as a col picture or co-located picture) that is spatially co-located with the current block. The co-located picture may be one picture of one or more reference pictures included in the reference picture list.

The derivation method of the motion information may be different according to the prediction mode of the current block. For example, the prediction modes applied to the inter prediction include AMVP mode, merge mode, skip mode, merge mode with motion vector difference, sub-block merge mode, geometric partition mode, combined inter-intra prediction mode, affine mode, and the like. Here, the merge mode may be referred to as a motion merge mode.

For example, when AMVP is used as a prediction mode, at least one of a motion vector of a reconstructed neighboring block, a motion vector of a co-located block, a motion vector of a block adjacent to the co-located block, and a (0, 0) motion vector may be determined as a motion vector candidate for the current block, and a motion vector candidate list may be generated by using the motion vector candidate. The motion vector candidates of the current block may be derived by using the generated motion vector candidate list. Motion information of the current block may be determined based on the derived motion vector candidates. The motion vector of the co-located block or the motion vector of a block adjacent to the co-located block may be referred to as a temporal motion vector candidate, and the motion vector of the reconstructed adjacent block may be referred to as a spatial motion vector candidate.

The encoding apparatus 100 may calculate a Motion Vector Difference (MVD) between a motion vector of the current block and a motion vector candidate, and may perform entropy encoding on the Motion Vector Difference (MVD). Further, the encoding apparatus 100 may perform entropy encoding on the motion vector candidate index and generate a bitstream. The motion vector candidate index may indicate the best motion vector candidate among the motion vector candidates included in the motion vector candidate list. The decoding apparatus may perform entropy decoding on motion vector candidate indexes included in the bitstream, and may select a motion vector candidate of the decoding target block from among motion vector candidates included in the motion vector candidate list by using the entropy-decoded motion vector candidate indexes. Further, the decoding apparatus 200 may add the entropy-decoded MVD to the motion vector candidates extracted by the entropy decoding, thereby deriving a motion vector of the decoding target block.

In addition, the encoding apparatus 100 may perform entropy encoding on the resolution information of the calculated MVD. The decoding apparatus 200 may adjust the resolution of the entropy-decoded MVD using the MVD resolution information.

In addition, the encoding apparatus 100 calculates a Motion Vector Difference (MVD) between a motion vector in the current block and a motion vector candidate based on the affine model, and performs entropy encoding on the MVD. The decoding apparatus 200 derives a motion vector on a per sub-block basis by deriving an affine control motion vector of the decoding target block from the sum of the entropy-decoded MVD and affine control motion vector candidates.

The bitstream may include a reference picture index indicating a reference picture. The reference picture index may be entropy encoded by the encoding apparatus 100 and then signaled as a bitstream to the decoding apparatus 200. The decoding apparatus 200 may generate a prediction block of the decoding target block based on the derived motion vector and the reference picture index information.

Another example of a method of deriving motion information of a current block may be a merge mode. The merge mode may represent a method of merging motions of a plurality of blocks. The merge mode may represent a mode in which motion information of a current block is derived from motion information of neighboring blocks. When the merge mode is applied, the merge candidate list may be generated using motion information of reconstructed neighboring blocks and/or motion information of co-located blocks. The motion information may include at least one of a motion vector, a reference picture index, and an inter-picture prediction indicator. The prediction indicator may indicate unidirectional prediction (L0 prediction or L1 prediction) or bidirectional prediction (L0 prediction and L1 prediction).

The merge candidate list may be a list of stored motion information. The motion information included in the merge candidate list may be at least one of motion information of a neighboring block adjacent to the current block (spatial merge candidate), motion information of a co-located block of the current block in the reference picture (temporal merge candidate), new motion information generated by a combination of motion information existing in the merge candidate list, motion information of a block encoded/decoded before the current block (history-based merge candidate), and zero merge candidate.

The encoding apparatus 100 may generate a bitstream by performing entropy encoding on at least one of the merge flag and the merge index, and may signal the bitstream to the decoding apparatus 200. The merge flag may be information indicating whether to perform a merge mode for each block, and the merge index may be information indicating which of neighboring blocks of the current block is a merge target block. For example, neighboring blocks of the current block may include a left neighboring block located at the left side of the current block, an upper neighboring block arranged above the current block, and a temporal neighboring block temporally adjacent to the current block.

In addition, the encoding apparatus 100 performs entropy encoding on correction information for correcting a motion vector among the motion information of the combination candidates, and signals it to the decoding apparatus 200. The decoding apparatus 200 may correct the motion vector of the merge candidate selected by the merge index based on the correction information. Here, the correction information may include at least one of information on whether to perform correction, correction direction information, and correction size information. As described above, the prediction mode in which the motion vector of the synthesis candidate is corrected based on the signaled correction information may be referred to as a merge mode having a motion vector difference.

The skip mode may be a mode in which motion information of a neighboring block is applied to a current block as it is. When the skip mode is applied, the encoding apparatus 100 may perform entropy encoding on information of the fact of which block's motion information is to be used as motion information of the current block to generate a bitstream, and may signal the bitstream to the decoding apparatus 200. The encoding apparatus 100 may not signal syntax elements regarding at least any one of motion vector difference information, an encoded block flag, and a transform coefficient level to the decoding apparatus 200.

The sub-block merging mode may represent a mode in which motion information is derived in units of sub-blocks of a coded block (CU). When the sub-block merging mode is applied, a sub-block merging candidate list may be generated using motion information (sub-block-based temporal merging candidates) and/or affine control point motion vector merging candidates of a sub-block located with the current sub-block in the reference image.

The geometric partition mode may represent a mode in which motion information is derived by partitioning a current block in a predetermined direction, each prediction sample is derived using each of the derived motion information, and the prediction samples of the current block are derived by weighting each of the derived prediction samples.

The inter-intra combined prediction mode may represent a mode in which a prediction sample of a current block is derived by weighting a prediction sample generated by inter prediction and a prediction sample generated by intra prediction.

The decoding apparatus 200 may correct the derived motion information by itself. The decoding apparatus 200 may search a predetermined region based on the reference block indicated by the derived motion information and derive the motion information having the minimum SAD as the corrected motion information.

The decoding apparatus 200 may compensate prediction samples derived via inter prediction using the optical stream.

Fig. 6 is a diagram showing a transformation and quantization process.

As shown in fig. 6, a transform process and/or a quantization process is performed on the residual signal to generate a quantized level signal. The residual signal is the difference between the original block and the predicted block (i.e., the intra-predicted block or the inter-predicted block). The prediction block is a block generated by intra prediction or inter prediction. The transformation may be a primary transformation, a secondary transformation, or both a primary transformation and a secondary transformation. The primary transform of the residual signal generates transform coefficients and the secondary transform of the transform coefficients generates secondary transform coefficients.

At least one scheme selected from among various pre-defined transform schemes is used to perform the primary transform. Examples of the predefined transform scheme include, for example, discrete Cosine Transform (DCT), discrete Sine Transform (DST), and Karhunen-Loeve transform (KLT). The transform coefficients generated by the primary transform may undergo a secondary transform. The transform scheme for the primary transform and/or the secondary transform may be determined according to coding parameters of the current block and/or neighboring blocks of the current block. Alternatively, transformation information indicating the transformation scheme may be signaled. DCT-based transforms may include, for example, DCT-2, DCT-8, and the like. The DST-based transformation may include, for example, DST-7.

The quantized level signal (quantization coefficient) may be generated by performing quantization on the residual signal or on the result of performing the primary transform and/or the secondary transform. The quantized level signal may be scanned according to at least one of a diagonal up-right scan, a vertical scan, and a horizontal scan according to an intra prediction mode of a block or a block size/shape. For example, when the coefficients are scanned in a diagonal up-right scan, the coefficients in the block form are changed to a one-dimensional vector form. In addition to the diagonal top-right scan, a horizontal scan that horizontally scans coefficients in the form of a two-dimensional block or a vertical scan that vertically scans coefficients in the form of a two-dimensional block may be used depending on the intra prediction mode and/or the size of the transform block. The scanned quantized level coefficients may be entropy encoded for insertion into a bitstream.

The decoder entropy decodes the bit stream to obtain quantized level coefficients. The quantized scale coefficients may be arranged in two-dimensional blocks by inverse scanning. For the inverse scan, at least one of a diagonal upper right scan, a vertical scan, and a horizontal scan may be used.

The quantized level coefficients may then be dequantized, then secondarily inverse transformed, if necessary, and finally primarily inverse transformed, if necessary, to generate a reconstructed residual signal.

Inverse mapping in the dynamic range may be performed for the luminance component reconstructed by intra-frame prediction or inter-frame prediction before in-loop filtering. The dynamic range may be divided into 16 equal segments and a mapping function for each segment may be signaled. The mapping function may be signaled at the stripe level or parallel block group level. An inverse mapping function for performing inverse mapping may be derived based on the mapping function. In-loop filtering, reference picture storage, and motion compensation are performed in the inverse mapping region, and a prediction block generated through inter prediction is converted to the mapping region via mapping using a mapping function and then used to generate a reconstructed block. However, since intra prediction is performed in the mapped region, a prediction block generated via intra prediction may be used to generate a reconstructed block without mapping/inverse mapping.

When the current block is a residual block of a chroma component, the residual block may be converted to an inverse mapping region by performing scaling on the chroma component of the mapping region. The availability of scaling may be signaled at the stripe level or parallel block group level. Scaling may be applied only when a mapping for the luminance component is available and the partitioning of the luminance component and the partitioning of the chrominance component follow the same tree structure. Scaling may be performed based on an average of sample values of the luminance prediction block corresponding to the color difference block. In this case, when the current block uses inter prediction, the luminance prediction block may represent a mapped luminance prediction block. The value required for scaling may be derived by referencing a look-up table using the index of the segment to which the average of the sample values of the luma prediction block belongs. Finally, the residual block may be converted to an inverse mapping region by scaling the residual block using the derived value. Chroma component block recovery, intra prediction, inter prediction, intra filtering, and reference picture storage may then be performed in the inverse mapping region.

Information indicating whether mapping/inverse mapping of the luminance component and the chrominance component is available may be signaled through a sequence parameter set.

The prediction block of the current block may be generated based on a block vector indicating a displacement between the current block and the reference block in the current picture. In this way, a prediction mode for generating a prediction block with reference to a current picture is referred to as an Intra Block Copy (IBC) mode. The IBC mode may be applied to m×n (M < =64, N < =64) coding units. IBC mode may include skip mode, merge mode, AMVP mode, and the like. In the case of the skip mode or the merge mode, a merge candidate list is constructed, and a merge index is signaled so that one merge candidate can be specified. The block vector of the specified merge candidate may be used as the block vector of the current block. The merge candidate list may include at least one of spatial candidates, history-based candidates, candidates based on an average of two candidates, and zero merge candidates. In the case of AMVP mode, a difference block vector may be signaled. Further, the prediction block vector may be derived from a left neighboring block and an upper neighboring block of the current block. An index of the neighboring blocks to be used may be signaled. The prediction block in IBC mode is included in the current CTU or left CTU and is limited to a block in an area that has been reconstructed. For example, the values of the block vectors may be limited such that the prediction block of the current block is located in the region of three 64×64 blocks before the 64×64 block to which the current block belongs in the encoding/decoding order. By limiting the values of the block vectors in this way, memory consumption and device complexity according to IBC mode implementations may be reduced.

Hereinafter, an image encoding/decoding method using a sub-block-based transform (sub-block transform) according to the present invention will be described.

The present invention improves coding efficiency by performing sub-block based transform (SBT) when transform is applied for image compression under specific conditions. The present invention can improve conventional coding techniques that may result in system complexity, lower coding efficiency, lower transmission efficiency, or lower image quality.

Further, when a transform is applied to an image under a specific condition, coding efficiency can be improved by not performing a sub-block based transform (SBT). At this time, the present invention can improve coding efficiency by considering the shape and size of a block under specific conditions.

Hereinafter, the transformation and the sub-block-based transformation may include an inverse transformation and a sub-block-based inverse transformation, respectively.

SBT represents a sub-block transform, which is one of transform techniques applicable to a residual signal obtained by subtracting a predicted image signal (or prediction signal) from an image input to an encoder.

SBT is applied to a residual signal or directly to an image input to an encoder. Therefore, the signal to which the SBT is applied is not particularly limited.

The encoded base unit may be referred to as an encoding unit (CU). The CU itself may be used as a unit for prediction, or may be divided into further subdivided units according to applications to perform prediction.

The unit performing the prediction may be generally referred to as a Prediction Unit (PU). Thus, one CU may be predicted as one PU, or a method of obtaining a prediction residual signal by dividing one CU into a plurality of PUs and obtaining a prediction signal in each prediction unit may be used.

In addition, instead of dividing one CU into a plurality of PUs, if a CU is divided into a CU having a smaller size such that one CU becomes one PU, one CU may become one PU. The encoding/decoding system can be implemented more simply by configuring one CU as one PU.

In this disclosure, for convenience of description, the techniques of this disclosure will be described under the assumption that prediction is performed by CU units (i.e., this means that one CU becomes one PU), unless otherwise specified.

In addition, since CUs are divided into smaller sizes, it is necessary to signal whether CUs are divided or not separately.

Therefore, when the partitioning is performed such that one CU becomes one PU in order to further simplify the system implementation, the amount of information indicating the CU partitioning may increase, thereby degrading the encoding efficiency. Fig. 8 is a diagram showing an example of division of CUs as encoding units.

Although the CU is not further divided, if the same effect as the further divided CU is obtained, the encoding efficiency can be improved without the above-described problem.

The present invention relates to a technique of a transformation method and apparatus designed to solve these technical problems. In addition, the present invention relates to an encoding method and apparatus using the transformation method and apparatus, a decoding method and apparatus, and a method and apparatus for constructing a compressed bitstream.

A residual signal obtained by subtracting a prediction signal from a coding unit signal input to an encoder may be transformed into transform coefficients by a transform for encoding.

The unit performing the transform is called a Transform Unit (TU).

For example, one CU may become one TU. That is, an input image signal of the encoding unit becomes a residual signal through prediction, wherein the residual signal can be converted into a transform coefficient through transform.

However, after one CU is divided into two sub-blocks without being used as one TU, the transform is applied to one sub-block and the transform is not applied to the other sub-blocks. The other sub-block has a value of 0. This may be referred to as zeroing (zeroing-out).

The encoder encodes and transmits the transform coefficients of one sub-block divided from the CU, and the decoder decodes and inversely transforms the transform coefficients that have been encoded and transmitted. However, since both the encoder and the decoder know that the other sub-block has a value of 0, general transform coefficient encoding or decoding may not be performed.

Although it has been assumed so far that zero (i.e., having a value of 0) is set for convenience of description, specific values other than 0 may be used. In this case, the specific value may be predefined by the encoder and the decoder, and the value may be determined and used for each sub-block and may be transmitted. The decoder may parse and decode the value.

That is, in encoding of a CU, there may be transform coefficients for only one sub-block of the CU, and the value may be considered 0 (or a particular value) for the other sub-blocks. Therefore, encoding is not performed, thereby improving encoding efficiency.

Fig. 9 (a) shows an example of a zeroing sub-block according to the SBT mode. Here, the sub-block represented in white indicates a zero-return sub-block without transformation.

Fig. 9 (b) shows an embodiment indicating an SBT mode using the cu_sbt_flag, the cu_sbt_quad_flag, the cu_sbt_horizontal_flag, and the cu_sbt_pos_flag.

The cu_sbt_flag, the cu_sbt_quad_flag, the cu_sbt_horizontal_flag, and the cu_sbt_pos_flag of fig. 9 (b) may be transmitted from the encoder to the decoder.

The information cu_sbt_flag indicating whether to use the SBT may indicate whether the current CU uses the SBT. This may indicate that the SBT is not used when the cu_sbt_flag has a first value (e.g., "0"), and may indicate that the SBT is used when the cu_sbt_flag has a second value (e.g., "1"). Thus, the encoder may determine whether all or part of the current CU is inverse transformed by parsing and interpreting the value of the cu_sbt_flag. When the value of the cu_sbt_flag is a second value (e.g., "1") (i.e., when SBT is used), the decoder may entropy-decode the cu_sbt_quad_flag as next information.

The SBT partition information cu_sbt_quad_flag may indicate a method of partitioning the current CU. That is, when the cu_sbt_quad_flag has a first value (e.g., "1"), this may indicate that the current CU is partitioned at 1:3 (or 3:1) (this is referred to as 1/4 partitioning), and when the cu_sbt_quad_flag has a second value (e.g., "0"), this may indicate that the current CU is partitioned at 1:1 (this is referred to as 1/2 partitioning). In addition, when the cu_sbt_flag and the cu_sbt_quad_flag are not entropy decoded, the cu_sbt_flag and the cu_sbt_quad_flag may be inferred to be a second value (e.g., "0").

Further, the decoder may entropy-decode the cu_sbt_horizontal_flag indicating a division direction for the sub-block.

The SBT partition direction information cu_sbt_horizontal_flag may indicate a partition direction for the sub-block. That is, when the cu_sbt_horizontal_flag has a first value (e.g., "1"), this may indicate that the current CU is divided into two sub-blocks in the horizontal direction, and when the cu_sbt_horizontal_flag has a second value (e.g., "0"), this may indicate that the current CU is divided into two sub-blocks in the vertical direction.

Further, the decoder may entropy-decode the cu_sbt_pos_flag.

The SBT position information cu_sbt_pos_flag may indicate which of two sub-blocks constituting the current CU is transformed. That is, when the value of the cu_sbt_pos_flag is a first value (e.g., "1"), a first sub-block located at the top (or left side) is transformed, and when the value of the cu_sbt_pos_flag is a second value (e.g., "0"), a second sub-block located at the bottom (or right side) is transformed.

As described above, other sub-blocks that are not transformed are set to zero (or a specific value).

Thus, eight SBT modes may be derived from information other than the cu_sbt_flag indicating whether SBT is used. An example of a combination of eight modes is shown in fig. 9 (a). In addition, examples of four flag values cu_sbt_flag, cu_sbt_quad_flag, cu_sbt_horizontal_flag, and cu_sbt_pos_flag for the eight SBT modes are shown in (b) of fig. 9.

In addition, in the descriptions of the cu_sbt_flag, the cu_sbt_quad_flag, the cu_sbt_horizontal_flag, and the cu_sbt_pos_flag, examples of the first value and the second value are not limited to the above description, and different values may be set according to embodiments. For example, when the value of the cu_sbt_pos_flag is a first value (e.g., "0"), this may indicate that a first sub-block located at the top (or left) is transformed, and when the value of the cu_sbt_pos_flag is a second value (e.g., "1"), this may indicate that a second sub-block located at the bottom (or right) is transformed.

The case where the SBT technique for dividing the CU in the minimum steps and obtaining the same effect as the further division is advantageous can be predicted according to the shape, size, or encoding state of the block or a channel such as YCbCr.

Therefore, if a specific condition between the encoder and the decoder is predetermined and when the condition is satisfied, the SBT is not used, so that the value of the cu_sbt_flag may be inferred to be 0 instead of transmitting information indicating whether the SBT (cu_sbt_flag), whether the CU is subjected to 1/4 division or 1/2 division (cu_sbt_quad_flag), whether the CU is divided horizontally or vertically to obtain a sub-block (cu_sbt_horizontal_flag), which of the two divided sub-blocks is transformed (cu_sbt_pos_flag). Therefore, the decoder can be informed of the non-use of the SBT without transmitting the above information, thereby improving the encoding efficiency.

In another method, a specific condition between the encoder and the decoder may be predetermined, and when the condition is satisfied, the predictable context information may be used for entropy encoding (e.g., arithmetic encoding or CABAC encoding) by further increasing (or decreasing) the probability of a specific value of the corresponding information when SBT related information (hereinafter, referred to as SBT information, e.g., cu_sbt_flag, cu_sbt_quad_flag, cu_sbt_horizontal_flag, and cu_sbt_pos_flag) selected by the encoder is entropy encoded (e.g., arithmetic encoding or CABAC encoding), thereby improving encoding efficiency or simplifying the encoder.

Similarly, if a specified condition predetermined by the encoder is satisfied, by further increasing (or decreasing) the probability of a specific value of the information when the decoder entropy-decodes (e.g., arithmetic decoding or CABAC decoding) the selected SBT-related information, the predictable context information for entropy decoding (e.g., arithmetic decoding or CABAC decoding) can be used as much as possible, thereby improving the encoding efficiency.

In another method, a specific condition between an encoder and a decoder is predetermined, and when the condition is satisfied, when SBT related information (cu_sbt_flag, cu_sbt_quad_flag, cu_sbt_horizontal_flag, and cu_sbt_pos_flag) selected by the encoder is entropy-encoded (for example, arithmetic coding or CABAC coding), the number of necessary contexts is limited to a predetermined number (1, 2, or 3), and the corresponding information is entropy-encoded using a limited number of contexts to perform entropy encoding using predictable context information as much as possible, thereby reducing complexity of the encoder while improving coding efficiency.

Similarly, if a specified condition predetermined by the encoder is satisfied, when the decoder entropy decodes (e.g., arithmetic decoding or CABAC decoding) the selected SBT related information (cu_sbt_flag, cu_sbt_quad_flag, cu_sbt_horizontal_flag, and cu_sbt_pos_flag), the number of necessary contexts is limited to a predetermined number (1, 2, or 3), and entropy decodes the corresponding information using a limited number of contexts to entropy decode using predictable context information as much as possible, thereby reducing complexity of the decoder while improving encoding efficiency.

Embodiments of the present invention devised to solve the technical problems described above will now be described.

Example 1 ]

In the present embodiment, compression efficiency can be improved by allowing non-use of the SBT to be recognized in advance between the encoder and the decoder under specific conditions without separately transmitting the cu_sbt_flag indicating whether to use the SBT. At this time, the specific condition may include at least one of a shape or a size of the at least one block. Alternatively, predefined characteristics of the blocks may be considered. Alternatively, whether a block is a luminance signal or a chrominance signal may be considered.

For a more specific example, when the block is a chrominance signal, SBT may not always be used between the encoder and the decoder without transmitting the cu_sbt_flag having a value of 0. That is, for the luminance signal, a method of transmitting information (e.g., cu_sbt_flag) related to whether or not to use the SBT may be used, and for the chrominance signal, it may be agreed that the SBT is not used between the encoder and the decoder, instead of transmitting information (e.g., cu_sbt_flag) related to whether or not to use the SBT.

The various implementations of example 1 may be implemented differently depending on how the specific conditions are set and used. Since the encoder and decoder know in advance under what conditions the cu_sbt_flag has a value of 0, SBT may not be used without transmitting the cu_sbt_flag value, thereby improving encoding efficiency.

Fig. 11 is a diagram showing a method of implementing embodiment 1.

Embodiment 1 may be implemented in various forms according to how the "condition check for suggested practice 1" of fig. 11 is determined between an encoder and a decoder.

1.1 (According to an example of the shape of the block) in this case, the encoder and decoder may determine not to use SBT in advance (or use SBT according to an embodiment) when the block has a specific shape. Thus, although the cu_sbt_flag is not transmitted, the decoder may not (or may not) use SBT. For this purpose, the "condition check for the proposed practice 1" may be implemented in various forms as follows.

< Conditional check for suggested practice 1 >

1.1.a(cbWidth!=cbHeight)

1.1.b(cbWidth==cbHeight)

1.1.c(cbWidth>=N*cbHeight)

1.1.d(cbHeight>=N*cbWidth)

Here cbWidth and cbHeight refer to the width and height of the current CU, respectively. In addition, inequality "= <" indicating that "less than or equal to" right side "on the left side is replaced with" < "indicating that" left side is less than "right side". Further, N is a value representing the aspect ratio, which is calculated by width/height and may be any one of at least 2, 4, 8, 16 or 32.

In the 1.1.A embodiment, if the condition (cbWidth |= cbHeight) is true, this means that the CU is not square. That is, if the condition is agreed between the encoder and the decoder, when the CU is square, the SBT may not be used although the cu_sbt_flag is not transmitted. That is, when cbWidth is equal to cbHeight, the cu_sbt_flag may not be transmitted, and the decoder may perform decoding without using the SBT technique by deducing that the cu_sbt_flag=0.

In the example using the condition of 1.1.B (cbWidth = cbHeight), when the CU is not square, the encoder and decoder do not use SBT without transmitting the cu_sbt_flag. That is, when cbWidth and cbHeight are different, the cu_sbt_flag may not be transmitted, and the decoder may perform decoding by deducing that the cu_sbt_flag=0.

In the example of 1.1.C, if the width of the CU is less than N times the height of the CU (similarly, in the example of 1.1.D, the height of the CU is less than N times the width of the CU), the decoder may perform decoding without using SBT by deducing that the cu_sbt_flag=0, although the cu_sbt_flag is not transmitted. By such an example, the encoding efficiency can be improved.

Fig. 12 is a diagram showing another method of implementing embodiment 1.

Embodiment 1 may be implemented in various forms according to how the "condition check for suggested practice 2" of fig. 12 is determined between the encoder and the decoder.

1.2 (According to an example of the size of the block) in this case, the encoder and decoder may determine not to use the SBT in advance (SBT is used according to an embodiment) when the size of the CU is greater than (or less than or equal to) the predetermined size. Thus, although the cu_sbt_flag is not transmitted, the decoder may not (or may not) use SBT. For this reason, the "condition check for suggested practice 2" indicating the condition for checking the size of the CU may be implemented in various forms as follows.

< Conditional check for suggested practice 2 >

1.2.a((cbWidth<N1)&&(cbHeight<N2))

1.2.b((cbWidth<N1)OR(cbHeight<N2))

1.2.c(min(cbWidth,cbHeight)<N3)

1.2.d(max(cbWidth,cbHeight)<N4)

1.2.e(cbWidth*cbHeight<N5)

1.2.f(cbWidth+cbHeight<N6)

1.2.g(cbWidth==N7&&cbHeight==N6)

1.2.h(cbWidth==N7&&cbHeight==N7)

1.2.i(log(cbWidth)+log(cbHeight)<N8)

In various embodiments, the inequality "<" indicating that the left side is "less than" the right side may be replaced with "= <" indicating that the left side is less than or equal to the right side. Further, N1 to N7 indicating the predetermined condition boundary value may be independently one of 2, 4, 8, 12, 16, 32, 64, or 128, and N8 may be one of 0, 1, 2,3, 4, 5, or 6. Further, N1 to N8 indicating the predetermined condition boundary value may be determined based on the maximum transform size information. Here, the maximum transform size information may be information signaled from the encoder to the decoder.

In embodiment 1.2.A, when the width and height of the current CU are not less than (or greater than) the predetermined boundary values N1 and N2, respectively, the SBT may not be used without transmitting the cu_sbt_flag. That is, in this case, although the cu_sbt_flag is not transmitted, the decoder may perform decoding without using the SBT technique by deducing that the cu_sbt_flag=0. This is because zeroing of sub-blocks of a size that is 1/2 or 3/4 of the size of the CU is highly unlikely to be advantageous when the size of the CU is larger than the predetermined size.

In an example using the condition of 1.2.B ((cbWidth < N1) OR (cbHeight < N2)), when both the width and the height of the current CU are equal to OR greater than the predetermined boundary values (N1 and N2), respectively, although the cu_sbt_flag is not transmitted, the decoder may perform decoding without using the SBT technique by deducing that the cu_sbt_flag=0. This is because, similarly to the case described above, when the size of the CU is larger than the predetermined size, zeroing of a sub-block whose size is 1/2 or 3/4 of the size of the CU is extremely unlikely to be advantageous.

In the example of 1.2.C, when the shorter length among the width and the height is equal to or greater than the predetermined boundary value N3, although the cu_sbt_flag is not transmitted, the decoder may perform decoding without using the SBT technique by inferring that the cu_sbt_flag=0. In the example of 1.2.D, when a longer length among the width and the height of the CU is equal to or greater than a predetermined boundary value N4, although the cu_sbt_flag is not transmitted, the decoder may perform decoding without using the SBT technique by inferring that the cu_sbt_flag=0.

In the example of 1.2.E, when the product of the width and the height of the CU is equal to or greater than the predetermined boundary value N5, although the cu_sbt_flag is not transmitted, the decoder may perform decoding without using the SBT technique by inferring that the cu_sbt_flag=0. The example of 1.2.E may be slightly modified to be implemented like 1.2.F or 1.2. I. In 1.2.I, when the sum of the logarithmic values of the width and height of the CU is equal to or greater than the boundary value N8, and in 1.2.F, when the sum of the width and height of the CU is equal to or greater than the boundary value N6, although the cu_sbt_flag is not transmitted, the decoder may perform decoding without using the SBT technique by deducing that the cu_sbt_flag=0.

In 1.2.G, when the width and height of the CU are not the predetermined sizes N7 and N6, respectively, although the cu_sbt_flag is not transmitted, the decoder may perform decoding without using the SBT technique by deducing that the cu_sbt_flag=0. In 1.2.H, when both the width and the height of the CU are not the predetermined size N7, although the cu_sbt_flag is not transmitted, the decoder may perform decoding without using the SBT technique by deducing that the cu_sbt_flag=0. In 1.2.I, when the sum of logarithmic values of the width and height of the CU is equal to or greater than a predetermined size N8, although the cu_sbt_flag is not transmitted, the decoder may perform decoding without using the SBT technique by deducing that the cu_sbt_flag=0.

1.3 In the case of a particular channel (or component) of the CU, the encoder and decoder may predetermine that SBT is not used (or that SBT is used depending on implementation), so that the decoder may not use (may use) SBT even though sbt_cu_flag is not transmitted. For this reason, "condition check for recommended practice 1" or "condition check for recommended practice 2" may be implemented in various forms as follows.

< Conditional check for suggested practice 2 >

1.3.a isLuma(compID)

1.3.b(!isLuma(compID))

1.3.c isChroma(partitioner.chType)

1.3.d(!isChroma(partitioner.chType))

1.3.e(compID==COMPONENT_Y)

Condition check- > (compID = component_cb) for proposed practice 1

1.3.g(compID==COMPONENT_Cr)

CompID is an abbreviation for component ID, representing a color component. compID may be one of 0, 1, or 2, 0 representing luminance, 1 representing Cb, and 2 representing Cr.

The isLuma () function of (1) below determines whether the component index is 0 to determine whether it is a luminance block or a chrominance block.

Further, the function of (2) has the same meaning as (1), but determines whether the current channel is a luminance channel or a chrominance channel in another format.

In addition, the isChroma () function of (3) may determine whether the component index is 1 or 2 to determine whether it is a luminance block or a chrominance block.

In addition, the function of (4) has the same meaning as (3), but determines whether the current channel is a luminance channel or a chrominance channel in another format.

isLuma(const ComponentID id)(1){

return(id==COMPONENT_Y);

}

isLuma(const ChannelType id)(2)

{

return(id==CHANNEL_TYPE_LUMA);

}

isChroma(const ComponentID id)(3){

return(id!=COMPONENT_Y);

}

sChroma(const ChannelType id)(4){

return(id!=CHANNEL_TYPE_LUMA);

}

Although only the cu_sbt_flag is described in embodiment 1, the present invention is not limited thereto. Embodiment 1 is similarly applicable to other information related to SBT, i.e., cu_sbt_quad_flag, cu_sbt_horizontal_flag, cu_sbt_pos_flag, and the like.

Example 2 ]

In the present embodiment, a method and apparatus for performing entropy encoding/decoding using at least one of a shape of a block, a size of a block, or information on neighboring blocks in entropy encoding/decoding of SBT information when an image is encoded/decoded will be described. An embodiment obtained by applying the present embodiment to the cu_sbt_flag is shown in fig. 13.

By setting the condition check for the proposed practice 3 of fig. 13, as in embodiments 1.1 and 1.2, the context reflecting the probability of occurrence frequency of SBT information values can be determined according to the size of the block or the shape of the block.

When CABAC (context adaptive binary arithmetic coding) or arithmetic coding is used, probability value information of a symbol to be entropy-coded is required. When entropy encoding symbols, which probability value to use is an important factor in compression efficiency. Which symbol has what value is closely affected by other information related to the symbol. For example, the probability value of the cu_sbt_flag may be closely affected by the size or shape of the current CU. The various values of other information (which may be referred to as contexts) that determine probability values that affect the corresponding symbol and the probability value of the corresponding symbol may be referred to as a context model. That is, the CABAC encoder/decoder may use a context model indicating a probability value of a symbol to be encoded according to a value of related other information, instead of using an arbitrary probability value. The CABAC encoder/decoder may perform arithmetic coding/arithmetic decoding by a series of processes of selecting a probability model for each symbol according to the context of the input symbol and adapting probability estimation using local statistics.

The SBT information has a binary value of 0 or 1, and a context model of the information about the SBT to be entropy-encoded is defined. The context model is a set of probability models for one or more binary bits of the binarized symbol and is selected from available models based on statistics of recently encoded data symbols. The context model stores the probability of each binary bit becoming a "1" or "0". The CABAC encoder encodes each binary bit according to the selected probability model. Thereafter, the selected probability model is updated based on the actual encoding values.

In order to improve coding efficiency, it is important to find out information that closely affects SBT information to be coded and set probability values for SBT information values to be coded according to various values. Therefore, if a more accurate and precise context model in which a large number of contexts are set is used, coding efficiency can be improved. However, as the number of contexts increases, the system complexity may increase.

Fig. 13 illustrates an embodiment of two contexts in order to encode/decode the cu_sbt_flag (or sbtFlag) value. The selection and use of which of the two contexts may be implemented in various forms.

In fig. 13, when the conditional statement checked against the condition of the proposed practice 3 becomes true or false, either context 1 (ctxidx=1) or context 0 (ctxidx=0) can be selected.

Therefore, it is important to set the condition check for the proposed practice 3 to become true under certain conditions and to become false under another condition.

In this technique, the condition check for the recommended practice 3 may be set like the condition check for the recommended practice 1 of 1.1a to 1.1.D, or the condition check for the recommended practice 3 may be set like the condition check for the recommended practice 2 of 1.2.A to 1.2. I. In another embodiment, an arrangement as 2.1.A or 2.1.B below is possible.

< Conditional check for suggested practice 3 >

2.1.a(cuWidth*cuHeight<=256)

2.1.b(cuWidth*cuHeight>256)

Here, although 256 is used as the predetermined value, another value 128, 64, or 32 may be used according to the application.

That is, when the SBT information is entropy-encoded (CABAC-encoded or arithmetic-encoded) or entropy-decoded (CABAC-decoded or arithmetic-decoded) by referring to the sizes cuWidth and cuHeight of the CUs and their correlation (i.e., the shape of the CU) or characteristics, an appropriate context may be selected and used, thereby improving compression efficiency.

Although only the cu_sbt_flag is specifically described in embodiment 2, the present invention is not limited thereto. Embodiment 2 is similarly applicable to other information related to SBT, i.e., cu_sbt_quad_flag, cu_sbt_horizontal_flag, cu_sbt_pos_flag, and the like.

Example 3 ]

As described above, in entropy encoding/entropy decoding of SBT information, a method and apparatus for performing entropy encoding/entropy decoding using at least one of a shape or size of a block or information on neighboring blocks may be implemented.

As described above, the cu_sbt_quad_flag (or sbtQuadFlag) indicates a partition method (i.e., 1/2 partition or 1/4 partition) of a block. If the value is 1, this may indicate that the given CU is subject to 1/4 partitioning, and if the value is 0, this may indicate that the given CU is subject to 1/2 partitioning. For the description of the present embodiment, it is assumed that cu_sbt_quad_flag is 1. In this case, as shown in FIG. 14, a given CU is subject to 1/4 partitioning, i.e., partitioned by 1:3 or 3:1.

One of the two sub-blocks obtained after the CU is divided in 3:1 or 1:3 has a smaller size and the other sub-block has a larger size. Since a sub-block having a larger size among the two sub-blocks has a zero value (may have a specific value other than 0 according to an embodiment), improvement in coding efficiency is very excellent, but if an erroneous determination is made, loss due to degradation in image quality may be more fatal.

For CUs with a large number of zeroed sub-block pixels (i.e. with a relatively large size), there is a very high probability of loss. To avoid this risk, an arithmetic coding (CABAC) context for 1/4 partition may be used alone when the size of the CU is equal to or larger than a predetermined size. This embodiment may be shown in fig. 15.

In addition, when considering the width (W or cuWidth) and the height (H or cuHeight) of the CU, if only one side is subjected to 1/4 division, the cu_sbt_flag may have a value of 1. If only one side can be subjected to 1/4 division, the probability that the value of cu_sbt_quad_flag is 1 is smaller than the case that both sides (height H and width W) of the CU are subjected to 1/4 division. That is, the probability trend of the division direction of the sub-block according to the shape of the sub-block is closely related to the shape of the block. To further understand this, the shape of the CU before division into sub-blocks will be described with reference to fig. 16.

Fig. 16 shows four cases where only one of W or H of a CU may be subject to 1/4 partitioning. The CUs of fig. 16 (a) and (c) are horizontally long CUs. Since the height of the CU is small, 1/4 division is not possible in the horizontal direction, and 1/4 division is possible only in the vertical direction. However, since these CUs are horizontally long, the probability of dividing these CUs in the vertical direction is expected to be slightly smaller. Also, the CUs of fig. 16 (b) and (d) are vertically long CUs, 1/4 division in the vertical direction is impossible, and 1/4 division is possible only in the horizontal direction. However, since these CUs are vertically long, the probability of dividing these CUs in the horizontal direction is expected to be slightly smaller.

In order to utilize these statistical properties in practical applications, when either the width W or the height H of a CU is smaller than the minimum size (e.g., 16) that can withstand 1/4 partition, entropy encoding/entropy decoding may be performed by reducing the probability that the cu_sbt_quad_flag indicating that the CU is subject to 1/4 partition has 1, thereby improving compression efficiency.

Thus, the technique may be shown to improve compression efficiency by reflecting this trend in context.

The condition check of fig. 15 for the proposed practice 4 can determine the context by reflecting the probability of occurrence frequency of SBT according to the size of block and the shape of block as in embodiments 1.1 and 1.2 above. That is, the condition check for suggested practice 4 may be determined and implemented as the condition check for suggested practice 1 of 1.1.A to 1.1.D, or the condition check for suggested practice 4 may be determined and implemented as the condition check for suggested practice 2 of 1.2.A to 1.2. I.

In another embodiment, the condition check for suggested practice 4 may be determined and implemented as the condition check for suggested practice 3 of 2.1.A or 2.1. B.

In another embodiment, the condition check for suggested practice 4 may be determined and implemented as in 3.1.A below.

< Conditional check against suggested practice 4 >

3.1.a(sbtHorQuadAllow&&sbtVerQuadAllow)

SbtHorQuadAllow may have a value of 0 or 1. The value may be 1 if the current CU may be subject to 1/4 partition in the horizontal direction, and 0 if not. That is, in a state in which the use of SBT is enabled, sbtHorQuadAllow may be set to 1 when the height (H or cuHeight) of the CU is equal to or greater than 16.

Similarly sbtVerQuadAllow may have a value of 0 or 1. The value may be 1 if the current CU may be subject to 1/4 partition in the vertical direction, and 0 if not. That is, in a state in which the use of SBT is enabled, sbtVerQuadAllow may be set to 1 when the width (W or cuWidth) of the CU is equal to or greater than 16. This is represented by the following equation. Here minSbtCUSize may have a value of 8.

Equation 1

sbtHorQuadAllow=(cuHeight>=(minSbtCUSize<<1))

sbtVerQuadAllow=(cuWidth>=(minSbtCUSize<<1))

Although only the cu_sbt_quad_flag is specifically described in embodiment 3, the present invention is not limited thereto. Embodiment 3 is similarly applicable to other information related to SBT, i.e., cu_sbt_flag, cu_sbt_horizontal_flag, cu_sbt_pos_flag, and the like.

Example 4 ]

When various CU partitioning concepts such as QTBT or QT-BT-TT are applied, a CU may be partitioned into sub-blocks having not only a general square shape but also rectangular shapes having various shapes and sizes. According to the partition shape of the CU, when the SBT is used, the probability tendency of partitioning the CU in a specific direction is high. Accordingly, by restricting the sbt_mode shown in (a) of fig. 9, determining the dividing direction, or determining the context for entropy encoding/entropy decoding the information indicating the SBT mode according to the shape of the CU, compression efficiency may be improved or system implementation may be simplified.

4.1 (An embodiment of selectively signaling the cu_sbt_horizontal_flag indicating the partition direction of the block) as a simplest embodiment, when the CU is square, the cu_sbt_horizontal_flag is transmitted to indicate the partition direction of the block, otherwise (i.e., the CU is rectangular), the SBT may be used by fixing the specific partition direction having the highest probability.

Fig. 17 is a diagram showing the shape and sub-block division direction of a CU.

As shown in fig. 17 (a), if the CU has a horizontally long rectangular shape (i.e., a rectangular shape having a width greater than a height), the horizontal division tendency may be much larger.

As shown in (b) of fig. 17, if the CU has a vertically long rectangular shape (i.e., a rectangular shape having a height greater than a width), the vertical partition tendency may be much greater. Thus, an embodiment taking this into account can be implemented as shown in fig. 18.

According to fig. 18, if the CU is square, a value of cu_sbt_horizontal_flag may be transmitted. This is because CUs are square, and thus it is not possible to know the specific trend of dividing CUs in the horizontal direction or the vertical direction to form sub-blocks.

However, if the CU is rectangular, the value of the cu_sbt_horizontal_flag may not be transmitted, and may be inferred and decoded by the decoder using the following method. That is, if the CU has a horizontally long rectangular shape, the value of the cu_sbt_horizontal_flag may be inferred to be 1, and if the CU has a vertically long rectangular shape, the value of the cu_sbt_horizontal_flag may be inferred to be 0, and then encoding or decoding may be performed.

Fig. 19 is a diagram showing the shape of a CU and an SBT mode.

As shown in fig. 19 (a), if the CU has a horizontally long rectangular shape, as described above, the tendency of selecting horizontally divided sbt_mode may be high.

However, in a specific image, as shown in fig. 19 (b), horizontally long rectangular CUs may be vertically divided. It can be seen that the heterogeneous object exists horizontally in the current CU, even though the CU may be further divided, the division of the CU is stopped after the CU is vertically divided. To take this into account, as shown in fig. 20, a context determination method of cu_sbt_horizontal_ flags may be implemented.

The condition check of fig. 20 for the proposed practice 5 can determine the context by reflecting the probability of occurrence frequency of SBT according to the size of block and the shape of block as in the above embodiments 1.1 and 1.2. That is, the condition check for suggested practice 5 may be determined and implemented as the condition check for suggested practice 1 of 1.1.A to 1.1.D, or the condition check for suggested practice 5 may be determined and implemented as the condition check for suggested practice 2 of 1.2.A to 1.2. I. In another embodiment, the condition check for suggested practice 5 may be determined and implemented as the condition check for suggested practice 3 of 2.1.A or 2.1. B. In another embodiment, the condition check for suggested practice 5 may be determined and implemented as the condition check for suggested practice 4 of 3.1. A.

Although only the cu_sbt_horizontal_flag is specifically described in example 4, the present invention is not limited thereto. Embodiment 4 is similarly applicable to other information related to SBT, i.e., cu_sbt_flag, cu_sbt_quad_flag, cu_sbt_pos_flag, and the like.

Example 5 ]

The SBT itself has good compression efficiency, but it may be difficult to predict whether to use the SBT according to image characteristics, in which direction 1/2 division or 1/4 division is performed in the case that the SBT is used, or which sub-block is zeroed.

The context modeler used in CABAC models the probability of a symbol (i.e., a flag of the SBT to be encoded (or decoded)) using a binary bit binarized by a binarization unit as an input.

Since syntax information of binary bits and information on neighboring blocks are required for probability estimation in addition to binary bits to be encoded/decoded, a separate calculation process is required to store and process them. Therefore, in view of the impossibility of easily obtaining whether SBT, SBT partitioning methods and directions are used, and sub-blocks to be transformed using neighboring blocks or already obtained information (these are collectively referred to as contexts or context variables), it may be advantageous to use various contexts in terms of improvement of compression efficiency. However, in this case, the complexity of the encoding or decoding system may increase. Thus, for flag information whose probability trend is predicted to some extent, it may be advantageous in terms of reducing system complexity to perform bypass encoding using a single context, using equal probabilities of 0.5/0.5 without context, using a small number of (1 or 2) contexts if possible, or without CABAC encoding/decoding (more generally, arithmetic encoding/decoding). In this case, since the amount of calculation required for various modeling, tracking, and updating of the probability of a symbol can be reduced, this may be highly desirable in terms of simplifying the system.

Whether the current CU uses SBT may be estimated somewhat probabilistically using the size of the block during encoding/decoding. That is, it can be assumed that the probability of using SBT is greater when the product of the width and the height of the CU is less than or equal to 256.

Further, even in such a case where cu_sbt_horizontal_flag indicates a division direction for a sub-block, the probability of the division direction to be selected can be estimated to some extent from the shape of the CU. That is, when a CU has a horizontally long shape, the probability of dividing the CU in the horizontal direction may be high. In most cases, the above assumption is statistically correct with high probability, but may not be the case from the image. In addition, since syntax information of binary bits to be encoded and information on neighboring blocks are required, separate calculation processing is required to store and process them. In addition, even in terms of the number of contexts, since processing a plurality of contexts requires a larger amount of computation than a single context, reducing the number of contexts can simplify the system. This may be very advantageous in practical applications.

Fig. 21 is a diagram illustrating an embodiment of a context determination method for entropy encoding (or decoding) of SBT information. In the SBT information shown in fig. 21, for example, a cu_sbt_flag indicating whether or not to use the SBT will be described.

In context 1 (hereinafter referred to as "context determination 1 (Context Determination 1)") for encoding/decoding cu_sbt_flag (or sbtFlag) shown in fig. 21, as shown, the size of a CU may be referred to when a context for encoding/decoding is selected.

In selecting a context for entropy encoding/entropy decoding the cu_sbt_flag in fig. 21, the size of the CU may be used as shown in context determination 1 below.

Context determination 1:

uint8_t ctxIdx=(cuWidth*cuHeight<=256)?1:0;

m_BinEncoder.encodeBin(sbtFlag,Ctx::SbtFlag(ctxIdx));

according to the context determination 1, during CABAC encoding/decoding of the cu_sbt_flag, a context may be set and used according to fig. 22. cbWidth and cbHeight may have the same meaning as cuWidth and cuHeight, respectively.

However, when the context shown in fig. 22 is used, since two (0/1) or three (0/1/2) contexts are used, the complexity of the system may be unnecessarily increased. To improve this, in another example, by using a single context or reducing three (0/1/2) contexts to two (0/1) contexts, the complexity of the system can be reduced without greatly affecting the coding efficiency. Alternatively, by using an equal probability of 1/2 for a flag value of 0 or 1, the unnecessary calculation amount can be reduced. This embodiment is shown in "context determination 1.1" and "context determination 1.2" below. In a practical implementation, context 1 (or "context determination 1") shown in fig. 21 may be replaced with "context determination 1.1" or "context determination 1.2".

Context determination 1.1 implementation Using a single context

m_BinEncoder.encodeBin(sbtFlag,Ctx::SbtFlag(0));

Context determination 1.2 implementation with equal probability

m_BinEncoder.encodeBinEP(sbtFlag);

The context may be set and used according to fig. 23 during CABAC encoding/decoding of the cu_sbt_flag according to "context determination 1.1" or "context determination 1.2".

In another embodiment, context 1 (or "context determination 1") shown in FIG. 21 may be replaced with "context determination 1.3". This is shown in "context determination 1.3" and fig. 24 below.

Context determination 1.3 implementation Using bypass encoding/decoding

m_BinEncoder.encodeBin(sbtFlag);

In another embodiment, the entropy encoding/decoding system may be simplified by reducing the number of contexts to reduce the total computational effort and not reduce compression efficiency. Specifically, in the present embodiment, for example, the cu_sbt_horizontal_flag will be described. Although the shape and division trend of the block are statistically analyzed and used as context information when the cu_sbt_horizontal_flag information is transmitted, the number of contexts may be designed to be reduced to simplify the system.

When the cu_sbt_horizontal_flag is encoded, a context may be selected in consideration of a division direction (i.e., a shape of a block of part 2 as in fig. 21). This can be expressed in terms of "context determination 2" as described below.

Context determination 2:

uint8_t ctxIdx=(cuWidth==cuHeight)?0:(cuWidth<cuHeight1:2);

m_BinEncoder.encodeBin(sbtHorFlag,Ctx::SbtHorFlag(ctxIdx));

That is, according to the "context determination 2", the context may be set and used during CABAC encoding/decoding of the cu_sbt_horizontal_flag. This is shown in fig. 22.

According to the present embodiment, in this case, the system design can be simplified while minimizing the influence on the encoding efficiency. That is, as described above, in the case where general context modeling of various values of setting other information (which may be referred to as contexts) affecting probability values of corresponding symbols and probability values of corresponding symbols is not performed, the amount of computation is significantly reduced by an equal probability method having equal probabilities of 0 and 1 or a bypass encoding method in which arithmetic encoding is not performed, thereby improving compression efficiency. Alternatively, in a model in which encoding and decoding of a corresponding symbol does not have a relatively large influence in the existing context model, the amount of computation can be reduced by reducing the number, and the same compression performance can be obtained, thereby improving compression efficiency. This is specifically described in "context determination 2.1".

Context determination 2.1:

uint8_t ctxIdx=(cbWidth<cbHeight)?0:1;

m_BinEncoder.encodeBin(sbtHorFlag,Ctx::SbtHorFlag(ctxIdx));

That is, 2.1 "is determined according to the" context ", the context may be set and used during CABAC encoding/decoding of the cu_sbt_horizontal_flag. This is shown in fig. 25.

In another embodiment, "context determination 2.2" or "context determination 2.3" is possible.

Context determination 2.2:

uint8_t ctxIdx=(cbWidth<cbHeight)?1:0;

m_BinEncoder.encodeBin(sbtHorFlag,Ctx::SbtHorFlag(ctxIdx));

context determination 2.3:

uint8_t ctxIdx=(cbWidth>=cbHeight)?0:1;

m_BinEncoder.encodeBin(sbtHorFlag,Ctx::SbtHorFlag(ctxIdx));

The condition check of fig. 25 for the proposed practice 6 can determine the context by reflecting the probability of occurrence frequency of SBT according to the size of block and the shape of block as in embodiments 1.1 and 1.2. That is, the condition check for suggested practice 6 may be determined and implemented as the condition check for suggested practice 1 of 1.1.A to 1.1.D, or the condition check for suggested practice 6 may be determined and implemented as the condition check for suggested practice 2 of 1.2.A to 1.2. I. In another embodiment, the condition check for suggested practice 6 may be determined and implemented as the condition check for suggested practice 3 of 2.1.A or 2.1. B. In another embodiment, the condition check for suggested practice 6 may be determined and implemented as the condition check for suggested practice 4 of 3.1. A.

Although only the cu_sbt_flag or the cu_sbt_horizontal_flag is specifically described in embodiment 5, the present invention is not limited thereto. Embodiment 5 is similarly applicable to other information related to SBT, i.e., cu_sbt_quad_flag, cu_sbt_pos_flag, and the like.

Referring to fig. 26, the decoder may obtain SBT usage information (e.g., cu_sbt_flag) (S2601). In particular, when the width of the current block and the height of the current block are smaller than the maximum transform size, SBT usage information may be obtained.

In addition, the step S2601 of obtaining SBT usage information may include deriving context model information (e.g., ctxInc) of the SBT usage information, and performing entropy encoding based on the context model information to obtain the SBT usage information.

Here, the operation of deriving the context model information of the SBT usage information may include deriving the context model information of the SBT usage information based on whether the area of the current block is greater than or equal to a predefined value. The predefined value may be 256.

Further, when the SBT use information indicates the use of SBT, the decoder may obtain at least one of SBT division information, SBT division direction information, or SBT position information (S2602).

Here, the SBT division information (e.g., cu_sbt_quad_flag) may indicate a method of dividing the current block for the SBT, the SBT division direction information (e.g., cu_sbt_horizontal_flag) may indicate a division direction for the SBT, and the SBT position information (e.g., cu_sbt_pos_flag) may indicate which sub-block of the sub-blocks divided from the current block is transformed based on the SBT division information and the SBT division direction information.

Further, the decoder may perform SBT on the current block based on at least one of SBT partition information, SBT partition direction information, or SBT position information (S2603).

Referring to fig. 27, the encoder may determine whether SBT is used for the current block (S2701).

Further, the encoder may encode SBT usage information (e.g., cu_sbt_flag) based on the determination of step S2701 (S2702). Specifically, when the width of the current block and the height of the current block are smaller than the maximum transform size, the SBT usage information may be encoded.

In addition, the step S2702 of encoding the SBT use information may include determining context model information of the SBT use information and performing entropy encoding based on the context model information to encode the SBT use information.

Here, the operation of determining the context model information of the SBT usage information may include determining the context model information of the SBT usage information based on whether the area of the current block is greater than or equal to a predefined value. The predefined value may be 256.

Further, when the SBT use information indicates the use of SBT, the encoder may encode at least one of SBT division information, SBT division direction information, or SBT position information (S2703).

In addition, the bit stream generated by the image encoding method of fig. 27 may be stored in a non-transitory computer readable recording medium.

The above-described embodiments may be performed in the same way in the encoder and decoder.

At least one or a combination of the above embodiments may be used to encode/decode video.

The order applied to the above-described embodiments may be different between the encoder and the decoder, or the order applied to the above-described embodiments may be the same in the encoder and the decoder.

The above-described embodiments may be performed for each luminance signal and each chrominance signal, or may be performed identically for the luminance signal and the chrominance signal.

The block form to which the above-described embodiments of the present invention are applied may have a square form or a non-square form.

At least one of syntax elements (flags, indexes, etc.) entropy-encoded in the encoder and entropy-decoded in the decoder may use at least one of the following binarization, inverse binarization, entropy encoding/entropy decoding methods.

Method of binarization/inverse binarization of the signed 0 th order exp_golomb (se (v))

Method of binarization/inverse binarization of signed k-th order exp_golomb (sek (v))

-Method of binarization/inverse binarization of unsigned positive integer 0 th order exp_golomb (ue (v))

-Method of binarization/inverse binarization of k-th order exp_golomb without sign (uek (v))

Fixed length binarization/inverse binarization method (f (n))

-Truncated Rice binarization/inverse binarization method or truncated unary binarization/inverse binarization method (tu (v))

-Truncated binary/inverse binary method (tb (v))

Context-adaptive arithmetic coding/decoding method (ae (v))

-Byte unit bit string (b (8))

-Binarization/inverse binarization method (i (n)) for integers with sign

-Binarization/inverse binarization method (u (n)) of unsigned positive integer

-Unitary binarization/inverse binarization method

The above-described embodiments of the present invention may be applied according to the size of at least one of a coded block, a predicted block, a transformed block, a current block, a coded unit, a predicted unit, a transformed unit, a unit, and a current unit. Here, the size may be defined as a minimum size or a maximum size or both of the minimum size and the maximum size, so that the above embodiment is applied, or the size may be defined as a fixed size to which the above embodiment is applied. Further, in the above-described embodiments, the first embodiment may be applied to the first size, and the second embodiment may be applied to the second size. In other words, the above embodiments can be applied in combination according to the size. Further, when the size is equal to or larger than the minimum size and equal to or smaller than the maximum size, the above-described embodiments can be applied. In other words, when the block size is included in a specific range, the above-described embodiments can be applied.

For example, when the size of the current block is 8×8 or more, the above-described embodiments may be applied. For example, when the size of the current block is only 4×4, the above-described embodiments may be applied. For example, when the size of the current block is 16×16 or less, the above-described embodiments may be applied. For example, when the size of the current block is equal to or greater than 16×16 and equal to or less than 64×64, the above-described embodiments may be applied.

The above-described embodiments of the present invention can be applied according to a temporal layer. To identify a temporal layer to which the above embodiments may be applied, a corresponding identifier may be signaled, and the above embodiments may be applied to a specified temporal layer identified by the corresponding identifier. Here, the identifier may be defined as a lowest layer or a highest layer or both of the lowest layer and the highest layer to which the above-described embodiments are applicable, or may be defined as a specific layer indicating that the embodiments are applied. Furthermore, a fixed temporal layer may be defined to which the embodiments apply.

For example, when the temporal layer of the current image is the lowest layer, the above-described embodiments may be applied. For example, when the temporal layer identifier of the current image is 1, the above-described embodiments may be applied. For example, when the temporal layer of the current image is the highest layer, the above-described embodiments may be applied.

The stripe type or parallel block group type to which the above embodiments of the present invention are applied may be defined and may be applied according to the corresponding stripe type or parallel block group type.

In the above-described embodiments, the method is described based on a flowchart having a series of steps or units, but the present invention is not limited to the order of the steps, and some steps may be performed simultaneously with other steps or in a different order. Moreover, those of ordinary skill in the art will understand that steps in the flowcharts are not exclusive of each other, and that other steps may be added to the flowcharts, or some steps may be deleted from the flowcharts without affecting the scope of the present invention.

The described embodiments include various aspects of the examples. Not all possible combinations for the various aspects may be described, but one skilled in the art will be able to recognize different combinations. Accordingly, the present invention may be subject to all alternatives, modifications and variations that fall within the scope of the claims.

Embodiments of the present invention may be implemented in the form of program instructions executable by various computer components and recorded in a computer-readable recording medium. The computer readable recording medium may include individual program instructions, data files, data structures, etc. or combinations of program instructions, data files, data structures, etc. The program instructions recorded in the computer-readable recording medium may be specially designed and constructed for the present invention, or they may be well known to those having ordinary skill in the computer software arts. Examples of the computer-readable recording medium include magnetic recording media (such as hard disks, floppy disks, and magnetic tapes) specifically structured to store and implement program instructions, optical data storage media (such as CD-ROMs, or DVD-ROMs), magneto-optical media (such as floppy disks), and hardware devices (such as read-only memories (ROMs), random Access Memories (RAMs), flash memories, and the like). Examples of program instructions include not only machine language code, which is formatted by a compiler, but also high-level language code that may be implemented by a computer using an interpreter. The hardware devices may be configured to be operated by one or more software modules to perform the processes according to the invention, and vice versa.

While the present invention has been described in terms of specific items such as detailed elements, as well as limited embodiments and figures, they are provided solely to facilitate a more general understanding of the present invention and the present invention is not limited to the embodiments described above. Those skilled in the art to which the invention pertains will appreciate that various modifications and variations may be made from the foregoing description.

Therefore, the spirit of the invention should not be limited to the above-described embodiments, and the full scope of the claims and their equivalents should be within the scope and spirit of the invention.

INDUSTRIAL APPLICABILITY

The invention can be used for encoding or decoding images.

Claims

1. An image decoding method, comprising:

Obtaining sub-block based transform (SBT) usage information;

Obtaining at least one of SBT division information, SBT division direction information, or SBT position information when the SBT usage information indicates that SBT is used, and

Based on at least one of the SBT partition information, the SBT partition direction information, or the SBT position information, SBT is performed on the current block,

Wherein the step of performing the SBT includes partitioning the current block into a plurality of sub-blocks based on at least one of SBT partition information or SBT partition direction information, and performing an inverse transform on a part of the sub-blocks among the plurality of sub-blocks based on SBT position information,

Wherein when the width of the current block and the height of the current block are smaller than a maximum transform size, SBT usage information is obtained,

Wherein, the step of obtaining SBT division direction information includes:

deriving context model information of SBT partition direction information based on a shape of the current block, and

Performing entropy decoding based on context model information of the SBT partition direction information to obtain the SBT partition direction information,

Wherein the SBT division direction information indicates a division direction for the SBT,

Wherein the step of obtaining SBT usage information includes:

When the product of the width and the height of the current block is less than 256, setting context model information of SBT usage information to a first value;

When the product of the width and the height of the current block is equal to 256, setting context model information of SBT usage information to a first value;

Setting context model information of SBT usage information to a second value different from the first value when the product of the width and the height of the current block is greater than 256, and

The entropy decoding is performed based on context model information of the SBT usage information to obtain the SBT usage information.

2. An image encoding method, comprising:

determining whether a sub-block based transform (SBT) is used for the current block;

Encoding SBT usage information based on the determination;

partitioning a current block into a plurality of sub-blocks to encode a portion of the sub-blocks when determining that SBT is used for the current block, and

When the SBT use information indicates the use of SBT, at least one of SBT division information, SBT division direction information, or SBT position information is encoded,

Wherein when the width of the current block and the height of the current block are smaller than a maximum transform size, the SBT usage information is encoded,

The step of encoding the SBT division direction information comprises the following steps:

Performing entropy encoding based on context model information of the SBT partition direction information to encode the SBT partition direction information,

Wherein the step of encoding the SBT usage information includes:

Entropy encoding is performed based on context model information of the SBT usage information to encode the SBT usage information.

3. A method for transmitting a bitstream, the method comprising:

A bit stream is transmitted and,

Wherein the bit stream is obtained by:

Encoding SBT usage information based on the determination;

Wherein the step of encoding the SBT usage information includes: